Teemo, the swift scout, is known around the league community as the most annoying champion in the game. Poison that seems to last forever, quick movement speed, and the most annoying frecking voice you have ever heard, all contribute to his reputation. With this being said, Teemo is also a very fun champion to play, and with solid skills, you can master this champion.
Masteries honestly do not matter for Teemo. I normally use thunderlords as my keystone, but the path you use to get there can vary based on your personal playstyle. Most players use a typical AP build, and that works well, but feel free to adjust it to your preferences.
(sorry for not having pictures) Teemo is a champ who relies on AP, so all items in your build should involve it. Most people start Doran's Ring, but this is TROLLMO, and I like to start Spellthief's edge. On your first back, unless your against Nasus, Pantheon, or any high AD champ with hard CC, build up to Nashors. Nashors gets you 80 AP, along with some nice AS for farming, which is key for Teemo, and I will go in depth on farming in the Farming chapter. After Nashors, build your Spell thiefs to the Frost Queens. This gives some nice stats to help Trollmo. After this is where your build will vary. I like to use Swiftness Boots, and I suggest you do the same. Liandry's Torment should be your next Item, as it makes your Shrooms even Trollier. Build landrys before boots if you really need the AP. After this, your probably in the 25 minute mark, so I like to build Rabodons Deathcap for insane AP. Lastly,build Zhonyas if against alot of AD, or Abysmal scepter if your against alot of AP.
Teemo is not the most team oriented champ in the game. Teemo relies on alot of farm. Especially TROLLMO. Trollmo needs to stay in lane and farm as much as possible. A decent match for teemo is about 7 farm a minute (210 by 30 mins). Your teamates will call you for help, but only help if your ahead in farm. Staying top lane during team fights works great, becuase when the fight is over, just go invisible and the other team will not find you.