Teemo is well known for poking and being annoying. Teemo is good split pushing and roaming around. This guide will not go to in depth with Teemo, but I'll explain my best to be a great Teemo player.

Blade of the Ruin King
A lot of Teemo players will get this because of the 40% attack speed the slow and the percent base health damage. Although the attack speed is good, this will only make your auto-attacks stronger leaving your (Q)Blinding Dart and (R)Noxus Trap untouched. You wont need the slow because if you really did need to slow your opponents you would just get Rylai's Scepter. The percentage health is not that strong but Guisoon's Rageblade is a good Ap Attack Speed item.

Hextech Gunblade
This item may seem good because it will give you both ad and ap, but Guisoon's Rageblade would be much more better. The spell vamp will be useless on you also. And Rylai's Scepter is a better item for slows

Runaan's Huricane
This item I would get on Teemo during season 5. But this is season 6 and the item has been reworked. It only gives you 30% attack speed and useless crit. And you don't need the 2 extra bolts for wave clear because you already have your shrooms. Guisooon's Rageblade is strong on Teemo and also gives you the aoe damage for clearing waves.

Berserk Greaves
I remember I would get this item on Teemo. While this is a stronger item on Kayle rather than Sorcerer Shoes, Sorcerer Shoes is simply a stronger item. You poison auto attacks will penetrate more, you (Q)Blinding Dart will do more damage and (R)Noxus Trap will shred so bad. If you play Udyr or Xin Zhao you won't normally see people getting Berserk Greaves. Same on Teemo, you don't need alot of attack speed, you'll do less damage.

Obviously the best lane for Teemo is top lane. Sure he can work at mid but he does consistent damage over time not really busty with cc. Some Teemo players will pick bottom lane apc. Teemo's rang is not that high and can get harassed with teemo doing magic while the adc using crit against you.