This build is mainly based around life steal and spell vamp which both work well with teemo.

with the marks in this build it is up to you what ones you go with out of spell pen or flat ap i personally go flat ap.

try your best to last hit, if you lane with the ad carry split the creep evenly, if you mid focus more on last hitting then harrasing.

early game is the hardest part of the game with this build as it is very expensive, try to die as little as possible and steal all your teams kills, or get your own. as long as you get fed early you will help more late game.

you should be doing decent damage by now if not just try to take a wave of creep by yourself to get more money, you should have your will of the ancients by now, and the reason this works is because when an enemy hits your mushrooms each time the damage ticks (every time there health goes down from the damage over time) you get health back unlike with your e when it is just the impact damage, so that should keep you alive as long as you put mushrooms in the most popular places eg. baron dragon ramps buffs and corners of lanes and anywhere in river.

now you should at least have 4 of your items and the game should be coming together for you even if you are losing you should be able to bring your team back.