Twitch jungle is admittedly never the most optimal pick, however that doesn't stop you from 1v9ing consistently if you're willing to put in the work. In fact, there are several Twitch jungle OTPs is Masters/GM! Plus, if you are like me and love the role and champion, then you will enjoy playing him no matter how terrible he is in the meta.

Pros:

• Very fun playstle
• Hypercarry
• Great ganks
• 1v9 epic kiting clip machine

Cons:

• Good junglers will make your life very hard
• Have to put in a lot of effort compared to meta junglers
• Bad when behind
• Vulnerable to invades
• Overly gank reliant
• Terrible pick if you can't kite

• When ganking a lane, ALWAYS enter with Ambush, waiting to stand in between the enemy laner and their own tower before attacking.
• Make sure you use Venom Cask AFTER your first auto attack coming out of Ambush. Try to throw the Venom Cask to where the enemy laner will run to escape your gank, ensuring that they get stacks of Deadly Venom.
• There is a delay between using Ambush and being camouflaged. If you use a Blast Cone immediately after Ambush, you will be camouflaged by the time you hit the ground.
• Similarly, you can Recall right after using Ambush for a stealth recall.

Keystone choices:

• Lethal Tempo is what I find myself taking most of the time. It scales the best from all of Twitch's rune choices, and having the ability to kite over 2.5 attack speed is a savior in extended fights.
• Press the Attack is an excellent rune for your level 2 gank. It remains very effective versus single targets, but it doesn't scale quite as well as Lethal Tempo. Do not let this dissuade you from building it however, as it is arguably Twitch's most consistent rune, as well as the best early.
• Hail of Blades is the only rune you should be running on AP Twitch, and is also a fun rune on AD. It is excellent when ganking, but suffers in extended fights.

Lesser Runes

For Precision, the only viable rune for slot 1 is Triumph. Presence of Mind is a rune for Twitch ADC, not jungle, since your jungle item nullifies any mana issue you may have had.
For slot 2, any of them are viable in certain situations, but I always run Legend: Alacrity.
Either Coup de Grace or Cut Down is viable in slot 3, depending on how tanky the enemy team is.

For Domination, Sudden Impact is the best choice. Similarly to Presence of Mind, Taste of Blood is a laning rune, useless for jungling.
Eyeball Collection is the best slot 2 rune, due to Twitch jungle's aggressive early game playstyle.
All 4 runes in slot 3 are viable. Treasure Hunter lets you snowball with items, Ingenious Hunter is incredible when paired with Galeforce, Zhonya's Hourglass, Crown of the Shattered Queen, or any of Twitch's active items, Relentless Hunter is great for roaming the map, and Ultimate Hunter is the best choice in games with a lot of teamfights.

Sorcery is also viable as a secondary rune path. Any combination of Nimbus Cloak, Absolute Focus, or Gathering Storm is good.

Before the Game

The first thing to do when playing Twitch jungle is to see which lanes will be the easiest to gank. For example, if you have a CC-heavy midlaner like an Anivia versus a vulnerable, immobile champ like Veigar, that lane should be gankable. Also important to note are summoner spells. If an allied laner has Ignite, that lane will be easier to gank compared to if they had Teleport. This goes both ways. An enemy laner with no Flash will be easier to gank than one with Barrier.

Early Game

Twitch typically starts Red Buff if he is looking to level 2 gank. Do this if there is a gankable lane after first buff, pinging your laners to freeze the wave for the gank.
Sometimes, it is not always possible to level 2 gank. In cases like this, it is best to do Blue Buff and Gromp after Red Buff, looking to either take Rift Scuttler or gank a lane after.
If you are not able to start Red Buff due to an invade, do Blue Buff into Gromp into Red Buff, looking for a gank afterwards.
Pre-15 minutes, Twitch should look to gank any enemies that are overextended, stacking Dark Seal in the process.

Mid Game

At this stage in the game, once Twitch has 2 or 3 items, you can look to solo punish people who are overextended. He plays very similarly to post-6 Evelynn, so ensure that people respect the threat of your ganks. If you have Spray and Pray, you can look to take riskier plays, being able to 1v1 most people in the game (unless they are turbo fed) or even 1v2, if you cut them off under your own turret, for example.

You should also look to take objectives with your team. If you know what side of the map the enemy jungler is on, take the neutral objective on the other side of the map, or look to push lanes and destroy towers for map pressure.

Late Game

This stage in the game is where Twitch truly shines as a champion. At 6 items, every teamfight should be won with proper engage and if you have Spray and Pray up. Be very careful not to int your shutdowns, position well, and make sure to take advantage of won teamfights/picks by securing Dragons or Baron afterwards. You should be able to determine the outcome of all but the most one-sided of games that drag on to this point.