FL (fixed limit) Texas Holdem is the cornerstone of Texas Holdem and all its types. This is where you need to start if you intend to be a good NL (no limit) or PL (pot limit) player, because this is the best place to learn the fundamentals, with the least amount of risk involved.
 
On top of that, FL Holdem will force good players do descend to a level closer to that of a rookie and try to win the game by hammering home the fundamentals: Counting outs, odds calculation, and starting hand selection. In a word, even if you’re a rookie, nobody will be able to push you around and to bully you into doing stupid things, by virtue of the fact that they’ll have their hands tied by the rules of the game.

As said above, FL pre-flop play is based on the most fundamental poker principles: always look for positive expected value situations and play as many hands out of these situations as possible. In the same time, avoid EV- (negative expected value), and try not to act on EV- hands at all.

If you can keep this up, you’ll walk away a winner. Expected value is based on a lot of factors in preflop play: position at the table, the different reads you’ve made on your opponents, your starting hand value, the action generated by you and by the other players. In FL, it doesn’t exactly take a genius to see where the EV+ (positive expected value) is.

What you have to understand about FL play is, that the initial EV you get on your hand is more important than it is in NL or PL. In NL and PL, you have a few tools at your disposal to create a EV+ situation out of something else, while in FL you can’t really do a lot in that respect.
Also, the value of the hands that you decide to take down the stretch should be really solid most of the time (except when playing short-handed or in a heads-up game) because you can basically count on many of the other players seeing the turn and the river on their hands.