Pazaak is KOTOR's primary minigame, and will be one of your greatest cash resources, assuming you have a little luck and the patience to reload your game when you hit a bad string of losses.
Tips
The rules of the game are fairly basic; check your Completed Quests entries in the menus to get the basics down. You can also hit up Mission for a tutorial any time you're on the Ebon Hawk.
High-stakes Pazaak will require a good deck. You'll find cards in various places throughout the game worlds, but the most reliable method of acquisition is to simply buy them. Between the cantina bartender on Tatooine and the shady Rodian in East Central Ahto on Manaan, you should be able to compile a deck consisting almost completely of +/-2, 3, and 4 cards; these are the cards that are, given the odds, going to be useful in the most number of situations. The game has an odd way of valuing cards; it may value a +/-1 over a +/-2, but the former card is going to be useful far less often than the latter.
The first rule of Pazaak is: tell no one about Pazaak. The second rule of Pazaak is: the house always wins, with "the house," in this instance, being the computer-controlled player on the other side of the field. Not literally always, of course, but unfortunately, the game is stacked in the computer's favor, since the player is always forced to receive the first card in the game. This will get you near 20 sooner than your opponent most of the time, forcing you to play a card or stand before your opponent does. In a game like Pazaak, being forced to take the first action is a severe disadvantage; if you stay on 19, for instance, your opponent will know exactly what he has to do to win or tie, and will dip into his reservoir of cards only when appropriate.
Unfortunately, there's absolutely no way to get around this built-in penalty of Pazaak's; you'll just need to suck it up and deal with it. Since the computer will always do its damndest to match or beat your score, you'll know that your initial score will have to be at or near 20 in order to win; unless your opponent busts by a huge margin, he'll almost always find a way to hit a 19 or 20 during the first few games, especially if he knows that you're sitting on an 18. The computer also has a suspicious habit of hitting natural 20s more often than you do; whether this is just luck or a way to prevent you from making 100,000 credits before leaving Dantooine is a matter of speculation.
If you get lucky and begin a game with a few low cards, you'll find that the computer will always stay on an 18 or better, and will usually play a card in order to hit 19 or 20. If your opponent has no more cards in his hand, he'll stay on anything better than 16, which gives you a pretty big margin for error. As we've said, though, there's no way to consistently ensure that your opponent draws higher cards than you, so you'll generally need to attempt to get to 19 or 20 and stay there, and hope your opponent can't match up or do better than you.
The third rule of Pazaak is: the first game is important, but less important than the last. You'll want to try and ensure that you have something in your hand when you get to match point; hoping for a natural 20 is rarely a viable game strategy. If you find yourself constantly running out of cards in the third round or later, you'll probably be better off if you play more conservatively in the first round or two. Try to hit to as close to 20 as you can manage, then let the computer waste its cards trying to beat your score. Even if you wind up going in the hole, card advantage becomes much more important as the game goes on, so if you can goad the computer into wasting a card or two to tie a score of yours in the middle of the match, you'll be stronger towards the end game.
For our money, the best side deck consists of three +/-2 cards, three +/-4 cards, and four +/-3 cards, although the numbers of each card doesn't matter as much as the fact that they're there: if you don't have enough +/-3's, replace those slots with other double-sided cards, not a +3 or a -3. Any double-sided card is generally preferable to a single-sided card, though this is less true of the extreme ends of the double-sided types. A +/-6, for instance, should be scrapped in favor of a +3, just because, due to the way the cards hit the table, you're more likely to find a use for it.
It's rumored that some of the Pazaak players will give you a unique reward for winning a certain number of times in a row; most of these rewards are extra cards. Kudos on Tatooine will usually not give you a reward, since beating him ten times in a row activates a bug in the game.