Hey dude, go download PokerStove. Spoon has some videos on how to use it here.
It's fine to make general assumptions about a player's range, you have to start somewhere. When you install a HUD (heads-up display) and start gathering stats and notes on players, then it will come a little easier since you'll be able to distinguish the nits from the taggs, the laggs from the maniacs, etc.