Teemos Q blinds the enemy for 2,5 seconds - effective against most adc´s like: Ashe and some others... I am using the Lich Bane because of the damage after a ability: A tactic is useful for 1v1 chases: imagine, you are hunted by a Ashe... She is Bronze V (i do not HATE bronzies) and you are Silver (I - V) [?] She is chasing you... She does not know Teemos/your abilities: she is behind you and she is attacking you. Walk into an bush, plant your ult [R] (the mushroom) wait for her to walk into that shroom and do this combo: "A" for autoattack "Q" for your (2,5 sec) blinding dart: A Q A R A A A and so on and so on... She cant do anything - because of the dart...
This is what i can say... Its in good memories of these plays. Hope for your best!

A tip for you guys: Teemo APC with Blitzcrank as support is (good)...

It now seems to be very dumb to use exhaust with Teemo on the MIDLANE, but i had some good experiences with it. I did some first-bloods with exhaust. My tactic for the
Teemo-MIDLANE-Exhaust-First-Blood was: I stood right in the middle of the midlane, i waited and some asked "Teemo support" ? Yes, it is possible too! Again: I stood in the middle of the MIDLANE, i waited and the other midlaner asked "Who is mid then?". This other midlaner looked for the enemy (my team). I auto attacked him a couple of times until he flashed. Then i used exhaust and i followed him and auto-attacked him. It worked. It is worth for one tower-hit.
Hopefully it helped you!