Be prepared to wait and sometimes get bored. You get dealt 1/3 the hands live that you do online, and many people like to ponder their decisions for longer than the 15-20 seconds allowed online, slowing down the play. You get to see the people you are playing with though so you can rely somewhat on tells
to back up a read. Games are usually more softer/wild than online also, even for the higher buy-ins, so expect your BB/100 hands to be somewhat higer (variance is also higher due to chasers and action). I've heard of games were the standard raise is 10 times the BB, meaning that a 1/2 table plays like 2/5 one.
I'd sit down at a limit table before to get the hang of things (announcing your actions, betting, posting blinds, tipping, etc.) since if you make a mistake (bet out of turn, misplace a bet, etc.) it won't be as costly. When you feel comfortable, sign up for the NL and go for it.