~Boots for mobility since you need to dodge stuff.
~ Fiendish Codex for AP mana regen and CD
~finish boots because you need mobility
~ Sightstone for a little hp and unlimited wards so you wont get ganked :D
~build Fiendish Codex into Nashor's Tooth for more CD AP Mana regen and attack speed :D
~ Giant's Belt for hp then Needlessly Large Rod for more ap, finish the Giant's Belt into a Rylai's Crystal Scepter for more the CC HP and AP... finish that Rabadon's Deathcap now
~Situational's: preferably i would grab the Iceborn Gauntlet for ap and armour and cc and the amazing sheen passive+aoe slow. like what's not to love? then grab a Banshee's Veil for hp and mr. The iceborn is for ad on other team banshees for generally more hp it's passive and mr for ap champs on other team. you could als grab Zhonya's Hourglass Abyssal Mask or voidstaff

~Q can blind enemies! use to get away or to blind an auto attack champion.
~W can use to get away or chase enemies
~E just dots them noobs like a baws.
~use your Rs as minion wards, be close by your shrooms, always lay them down. Kite them around your shrooms c:
~don't engage team fights, your teemo they hate you and you're so cute a squishy they will be sure to focus you first.