I would add that if you are playing NL, you'll want to have starting requirements that are higher than what you'd play in Limit. In limit, depending on your position, two suited cards can have +EV, where as in NL a good player is going to raise enough post-flop to make drawing to a flush very expensive if you don't have outs to other draws. GSiHE is good, if you like NL, Harrington on Hold'Em is great. Playing hands with low EV or even marginal EV means you have to be much much better at reading your opponents post-flop.

S