Please look to the third build first

Alright. Your a rat. A damn rat that shoots people! What's not to love? Did I mention that your invisible to the naked eye? Even better!

This is my first guide and it will be on the champion Twtich. First thing, I play a very passive Twitch later on in the game, but to start with I am very aggressive. I have been playing him for a few months and he is by far my favorite champion to play. I hope you enjoy this guide, and feel free to give it ratings and suggestions.

-Dave

As Twitch, you have a number of pros and cons. Here is a short outline of them.

Pros:
-Stealth
-Ranged
-Good Burst Damage
-Can escape from messy situations with stealth
-Can scout ahead of your team

Cons:
-Squishy
-Oracles/Wards can ruin you
-Can be killed easily with Hard CC (Stunts, snares, knockups etc.)

There are a number of runes that can be very useful for Twitch. However the main ones that are of most use for Twitch are Attack Speed, Crit Chance, Attack Damage and sometimes Armour Pen.

Rune Build #1
Greater Mark of Attack Damage x9
Greater Seal of Attack Speed x9
Greater Glyph of Critical Chance x9
Greater Quintessence of Attack Damage x3

Rune Build #2 (Armor-Be-Gone)
Greater mark of desolation x9
Greater Glyph of Critical Chance x9
Greater Seal of Attack Speed x9
Greater quintessence of desolation x3

I normally pick Ghost and Cleanse. This gives you a lot of survivability. You can use this to be aggressive and chase down enemies.

Cleanse can be used for to save your hide and is perfect with ghost. Use in in the nasty ults that would otherwise root you or slow you.

Ghost can be used to run away, or catch up to an enemy. It can also be used while using Ambush, making it perfect for escaping from sticky situations or getting to your allies for a gank.

Heal can be used early game to help both yourself and your teammate when they are low health. Don't use it when they are missing a little bit of health, but when they are around 40% hp. I've also used this to tower dive and run away. However, don't use it over your ghost and cleanse as it is very week during late game.

Ignite is fine. I don't use it a lot as Twitch because of the poison and Expunge to finish them off.

Exhaust can be used to slow targets and make AD characters do a little less damage. You can slow them down with your AoE slowdown ability, so I don't find this as interesting.

Flash I find is a lot better in 3v3s then 5v5s. It can save your hide, or possibly get yourself the kill.

Teleport This can be used to teleport in to help your allies, or stop a lane from being pushed. Not as good as the others but still has it's uses.

Deadly Venom
Your passive will help your abilities do a lot more damage, or have better effects. It also does a nice amount of damage to your target and is most effective early game for harassing.

Ambush
This is a great ability. You can go completely invisible to your enemies for a short period of time at low levels (10 seconds), and at max level can last for a little under a minute! (50 seconds). This also gives you attack speed depending on how long you where in stealth. When your in combat, remember that this ability will take a lot longer to use. Try to go away from battle before using it. Use it to face check bushes early on, but be weary when they get an oracle or an ability that can see you (Tf's ult).

Expunge
Use this ability to finish of those that attempt to flee your ratty claws, or are at about 10-20% hp. You don't need to always use this when they are low health, but if you are going to use it before they are low health, try to get 3-6 stacks of your poison on them so it can do max damage.

Venom Cask
I find this the ability somewhat useless. It is not to say, completely useless. It has a 30% slowdown to start with but also scales with your stack of poison. I get it early game just to make it easier to get away or slow down fleeing enemies. When ganking and fighting in team fights, I use it after I break my stealth and pop my ult. I wait for about 2-3 shots and hit it. This will slow them, making wounded allies the ability to flee. By the end of the fight, it can be used again to stop the fleeing enemies.
I will max this out last however.

Spray and Pray
This is your ult. It is very powerful, and can easily whittle down half your enemies team health in seconds. When used, you gain a little bit of attack damage, the ability to pierce through units. You also gain a lot of range on your attacks. Use this after leaving stealth, gaining the attack speed buff, and the element of surprise. Before you leave your stealth try to position yourself in line with the enemies to get as many of them in possible with your attacks. With the extended range, you can save yourself from tower diving low hp enemies, or get low health turrets if needed. Remember to laugh manically when using this ability.

Order of use when Team Fighting or Ganking:

Ambush before the fight, line up so that as many enemies as possible will get hit with your ult.
Spray and Pray with your enemies lined up.
Debilitating Poison when at about 3-4 stacks of poison on each target.
Expunge when they have low health or 6 stacks of poison.
Ambush if you start getting hit

Here is a picture I made for this guide. Feel free to use it and spread it around, just make sure you link them here.

Early Game
Early game you want to get as many last hits as possible. This will give you the bonus gold which you WILL need. Start off with bugging your enemy with auto attacks when ever you can. This will discourage your enemy from advancing. Be careful of high CC champions, as if you do this to often you will find yourself stunned and dead. (Please look to earlier in the guide for champions with high CC). Once you get some boots and maybe your first item (Zeal, Vamp, Cloak and Dagger), you should start to roam a bit. Make sure that you tell your lane partner about this ahead of time. Try to go to lanes that seem to be in a stand-sill or are getting pushed back. This will help your team on their way to victory.

Mid Game
Your enemies should be getting wise to your antics and more then likely have wards and oracles. When this happens make sure you make a mental note of where you have seen them placed, and who has an oracle and who does not. Try to get your team mates to help you with the ones with Oracle's Elixir, and if you noticed wards, get an Oracle's Elixir yourself and find them. This works well when fighting vs [[Teemo] and other stealthed characters. If you notice a team fight about to start, rush to the locate and scout it out for your mates. When the fight starts, wait until your mates have engaged. Then line yourself up and attack. After the fight you should be looking for enemies that are attempting to recall in bushes and such. If they have low health that are a free kill.

Late Game
By this time, if you are doing well they WILL have wards and Oracle's Elixir. Do the same as mentioned above for this but try and scout out as much as possible, look at the buffs, the bushes, Baron and Dragon. By this point you should be easily taking half the HP off enemy champions, but remember, do not attack before your team does.

To help with common warding spots, please refer to the picture below:

I start off with a Doran's Blade. This gives you a nice attack damage increase, which is helpful for early game harassing and life steal and health to stay in lane longer. Or, if I know I will be getting bugged from the enemy team in lane I will take Boots and 3 Health Potion From then on I get:

Boots:
Boots are completely situational. Get them depending on the team composition of the enemy accordingly.

Berserker's Greaves
This gives you the attack speed and the movement speed, which is always nice as Twitch.

Mercury's Treads
If you notice a heavy CC team or find yourself hit a lot with it these will make your very squishy life a lot better.

Mobility Boots
Not my favorite, but it can be very helpful when your in stealth. This will make you zoom around the battle field, but only when your out of combat, which I find a downfall because you miss any other bonuses.

After boots:
The items here are the base work for your Big Items in the next section. Feel free to build them as you wish however.

Vampiric Scepter
Get this if you notice the enemy is out harassing you and you are always missing a lot of health. With your auto attack speed increase, this will make sure you have enough health to stay in your lane. Only get this if you do not get a Doran's Blade first.

Cloak and Dagger
Amazing item, not only give you attack speed, and crit, it allows you to escape CC more often. It has to be bought early game to be effective however.

Zeal
This gives a lovely well needed attack speed, crit chance, and movement speed. Get this after your Vampiric Scepter, or before it if you see fit.

Big Weapons
These will be the foundation of your build. The items here are the most damaging of the items in build and will help you further you damage against the enemy.

Infinity Edge
This is a great item for Twitch. Giving a ton of attack damage and crit chance, with a passive that increases your crits damage it will give you the needed attack damage. To start it off I normally get either the Pick Axe or B.F. Sword for the attack damage I am normally lacking. Complete it and move on to the next one.

Frozen Mallet
Let's face it. Your squishy. Very squishy. This gives you a lot of health, a % of attack damage, and the ability to passively slow your enemy down. Start by building a Phage. When you have your item, you will notice a large increase from your normal 1.6kish health, to your now 2.5k health. Worth it? Yes.

Phantom Dancer
Build this by using up your Zeal. This will give you a lot of attack speed, crit and a little bit of movement speed. Your now, even without a high movement speed boots, zooming around the battle field in and out of combat, helping you escape or catch up. When used with Ghost and your slow, you will be very hard to catch up to.

Bloodthirster
Build it off your Vampiric Scepter. This give you more attack damage, a little bit of life steal to keep you in the fight. When fully stacked this item gives you a ton of each. Also remember to line your self up with more minions in team fights, as the life steal from your ult's penetration will heal you a lot more. The main problem with this is that you need to farm a little bit of minions when you first get this.

Defensive Items
It will be important to take at least one of these. Do not wait until you have to take your item slot to pick a defensive item. It would be a wise idea to take a defensive item mid game where casters are melee are starting to do a lot of damage.

Wit's End
Because of a recent patch, this is a great defensive item for Twitch! It gives you attack speed and every time you attack you gain bonus magic resistance. Good for use against a magic heavy team

Banshee's Veil
Getting stunned a lot? Hate getting ulted by WW? This is the item for you! Gives a nice bit of magic resist. The main point of this item is the use of it's passive. Every so often, you will be immune to one spell. Although it is ONLY one spell, It also recharges fast. In this way it can be very useful, possibly saving your hide more then once.

Guardian Angel. Helps if you notice you die a lot. Also gives some armor and magic resistances! Getting this items means when you die you get a second chance at life, by this means, you could say, finish off a group of people, or get away. This does not mean your invincible, as you will come back at around 40% health. Still not as great as the Banshee's as you will still die if they guard your body while you rez.

Quicksilver Sash. Works well if the opposite have lots of hard CC. Also gives a nice of magic resistance. Don't underestimate this time, It can save your butt more often then you think.

Hexdrinker. I find this a must if the enemy team has a Karthus. Otherwise it is useful as it give you the magic resist and can save you from duration over time spells that would normally end you life.

Possible Items of Value
These items may be valuable to you, however I do not suggest that you have to have them in your build.

Atma's Impaler. Could be useful as it give armor. The passive easily gives you around 50 attack damage if you have 2500 health. A well rounded item if you ask me.

Executioner's Calling. Can be used if you do not take an ignite, but is horrible late game and is better replaced with another. Get it early game if you wish.

Tiamat. This allows you to farm minions better. Gives decent damage, mana and health regeneration. Better items out there still.

Avarice Blade. Good for getting some gold early game and can be build into the next item.

Youmuu's Ghostblade. Good armor penetration, a little attack damage, crit and more importantly cool down reduction and an active passive. When activated, it gives you 20% faster movement speed, and 50% more attack speed.

Last Slot

Depending on the enemy team I either choose from the following:
Bloodthirster. More life steal, more damage.
Phantom Dancer. Attack speed, crit, movement speed.
Madred's Bloodrazor. Use this if your enemy has a lot of high health champions. It gives you attack speed, 30 attack damage, and some armor.

If they have alot of armour:
Black Cleaver. Gives you a nice 55 attack damage, some attack speed and a stackible (Up to 3 times) armor debuff. Use this if they don't have ALOT of armor.
Last Whisper. Gives you 40 attack damage, and lets you negate 40% of the armor. Use this if they have a super armor tank.

All in all, you can flexibly change up this build to suit your needs, changing which item you take first or just getting a completely different item all together.

-Rank Expunge ASAP
-Rank ult when ever possible
-Ambush to facecheck bushes
-Attack speed is your friend!
-Your squishy, don't engage
-When walking through the forests, stealth for your safety.
-Use your slow to catch running enemies or stop them from getting you, or your team
-Watch the stacks of your poison on the enemies
-Line up your ult, the more you hit, the more damage you do
-When using your ult, it works with your life steal
-Help out your team mates, go gank high priority targets
-Try to lane with a tank, or someone with a nice amount of CC
-Harass early game

I am currently rank 30. I have played over 400 games so far, and I can say without an issue the game gets easier the higher you go up in levels. The only issue I have ever faced is horrible teammates. Just try your best and help your team.

Level 19. With a few level 30 friends also.
Level 23. With 3 friends and a pug.
Level 25. With one friend, and a KSing Ak.