Basically brad, this is what I do, but it kinda changes depending on whether the team itself is armor or magic resist. also has alot to do with who you lane against. If it's someone that is messing you up, you want to stack a bit of health early on, and if it's someone that you're having good luck with, just pile on the ap.

Some people want you to start with Rod of Ages, and a Mejai's Soulstealer. I die too much to really get any use of of the Soulstealer, however, the Rod of Ages is good for a champion that you're taking a bunch of damage from.

Something else, nothing says you have to get the items in this order. I might go straight to a nashor's tooth because the enemy is fairly squishy, and I can deal out alot more damage in a short amount of time rather than spread out over a long time.

After you have all the items you want, your mushrooms will be doing 1000 damage, and your toxic shot will be doing over a hundred damage per hit, then something like 50 damage per second for 4 seconds. It's not the burst damage that you're used to with the machine gun teemo you've been playing, but it's definitely awesome against squishy champs, and nothing feels better than an enemy champion to escape, only to die to your poison, or to a well placed mushroom.

Something else to consider is when you face off against someone, and you plan to duke it out 1 on 1, you always need to be spamming blinding dart when it's up, and try and drop a mushroom on top of them. They will either move which lets you attack them while they aren't attacking you, or they will stand there, which is awesome for you because it's beaucoup damage for you on top of what you're already doing, and if things look like they are going south, they now have a slow debuff on them so you can speed away or flash away, or any of the combination.

This is not what most of the other guides are going to do, in fact, it's pretty contradictory to most of what I've seen, but it works well for me.