If you are reading this guide now (I guess you do), you should know few simple requests:
1. If you don't agree with my builds/tips justify your opinion in comments.
2. This is build I use, I don't guarantee this will work for you as good as for me.
3. My english is not perfect, so don't judge me for mistakes.
4. This is my first guide, so if you have any suggestions of improving it - write a comment.

Thanks and enjoy!

Hi, this is my guide of Blitzcrank The Great Steam Golem. This is one of my favourite champions in LoL so far and here I'll try to show you my way of playing him.

Pros

+ Awesome ganker
+ Decent defender
+ Good initiator
+ Great disable abilities
+ Very mobile
+ Mass silence
+ Fun to play

Cons

- Grab is hard to master
- Requires good teamplay
- Long cooldowns

I use Flash + Ignite combo:

Flash - is awesome chasing/escaping ability, but main reason I use it is Flash + E combo
Ignite - as you probably know it is great finishing ability, I mostly use it to finish my grabbed victim

Other spells:

Cleanse - can be useful if enemy team has a lot of disables
Clairvoyance - it can help you to check invisible places (bushes, dragon, nashor) and aim for a grab
Clarity - it's not useful anymore after 5 mins, when you get Tear of the Goddess
Exhaust - not very useful, blitz has enough chase/escape abilities itself
Ghost - hmmm, maybe just use Overdrive
Teleport - since you got Overdrive you are mobile enough to run around the map
Fortify - it can be useful when you hook someone to the turret, also helps to last minions early
Rally Revive Smite Heal - no need anything to comment here

I use 3/24/3, 2% increased critical strike chance from Offense tree, small regeneration boost from Utility and rest 24 points on Armor. Basically most of the games blitz act like a tank, so armor and health bonus is always useful.

Mark
Greater Mark of Desolation - 1.66 armor penetration is best choice for blitz.
Greater Mark of Critical Chance - 0,93% critical chance is an option too, combined with Trinity Force this can be dangerous for your enemies.

Seal
Mainly here is competition between Greater Seal of Vitality and Greater Seal of Evasion, health boost is slightly better versus casters (AP) and dodge versus auto-atackers (AD).

Glyph
Greater Glyph of Cooldown Reduction and Greater Glyph of Scaling Cooldown Reduction are best for blitz in this group. It's actually your own decision, if you want early game advantage take Greater Glyph of Cooldown Reduction and if you think you will reach level 18 until game end pick Greater Glyph of Scaling Cooldown Reduction. I usually choose Greater Glyph of Scaling Cooldown Reduction.

Quintessence
Well, here is a lot of choice, so it depends from your playing style more. Greater Quintessence of Evasion can be great decision if combined with Greater Seal of Evasion, Greater Quintessence of Critical Chance can work perfectly with Greater Mark of Critical Chance, Greater Quintessence of Desolation is very usefull versus tanky enemies and Greater Quintessence of Health mixed with Greater Glyph of Cooldown Reduction gives you huge early game advantage. Anyway my vote here goes to Greater Quintessence of Vitality, which combined with Greater Seal of Vitality gives you 320 health bonus in late game.

You can see my skill sequence at the top of this guide, so I will try to explain it a bit.

Rocket Grab - is the main skill of blitz, so it should be your first pick versus any team. When you reach level 2 pick Power Fist. The combination of Rocket Grab and Power Fist is the Blitzcrank key of success. At the beggining of game try to only last-hit minions, let your enemies push. After you are level 2, try to grab enemy to your turret and smash him with Power Fist. Turret should make at least 2 hits to the enemy champion and if there is any doubt he can escape - use Ignite to finish him. After you are level 3 pick Rocket Grab again. Level 4 it's time to take Overdrive. Level 5 again go for Rocket Grab. Level 6 it's time for your mass damage/silence Static Field, which is great skill for farming waves of enemy minions. Level 7 - Rocket Grab again. Then I like to max Overdrive instead of doing it with Power Fist. Main reason of that is that Power Fist gets only cooldown reduction with each level and Overdrive gets efficiency increased.

Beggining:
Usually I start with: Sapphire Crystal + 2x Health Potion. Then after first comeback get Tear of the Goddess and Boots, if you have any gold left take few Health Potion, which is always useful.

Other situation is if you are solo lane versus 2 champions. Then start with Regrowth Pendant + Health Potion for longer survival in lane. After comeback buy Philosopher's Stone + Boots and start making Tear of the Goddess. Like in first build get few Health Potion if you have any gold left.

Shoes:
I usually buy Mercury's Treads or Ninja Tabi, depending if there is any casters in enemy team or not. Sometimes if you are not main tank in your squad or you are clearly dominating the game you can buy Boots of Swiftness too.

Manamune:
This is main item of blitz becouse of Mana Barrier, you should get it as fast as you can and use your abilities and atack to charge it.

Sheen:
Sheen gives you a huge damage burst. Combined with Manamune and Power Fist you can destroy your enemies with few hits.

Banshee's Veil:
Very useful item like for all other tanks. Spell block ability, + solid health, mana and magic resistance bonus is always welcome.

Trinity Force:
Great item to increase efficiency of Sheen + gives you a nice bonus of other stats.

Frozen Heart:
Great defensive item, if your enemies are auto-atackers (AD) you can buy it even before Trinity Force. Almost forgot 20% cooldown reduction which is very useful for blitz too.

Guardian Angel:
After you are true beast Guardian Angel can make you absolutely undefeatable.

1. Use Rocket Grab and Power Fist to pull enemy champions to your turret and kill them.
2. Use your Mana Barrier to easy farm waves of enemy minions.
3. Use wards in dragon, nashor, blue golem areas to detect enemies for a gank.
4. Use Rocket Grab to pull blue or red buff monsters through the obstacle to kill them faster and safer.
5. Interrupt your enemies channelling spells with Rocket Grab, Power Fist or Static Field abilities.
6. Use Flash + Rocket Grab combination.

Blitzcrank is a mobile,tanky fighter with unique ganking and disabling abilities. It's also one of most fun to play champions in the game so far. Anyway Blitzcrank requires lot of practice to control it properly. Hope this guide will help you in the game. I will try to update and improve it. If you have any questions, suggestions or comments post them below and I will try to answer them.


Good luck grabbing your enemies!