Low Limit Omaha
There is another version of Omaha called Omaha hi-lo. In this game the high hand and low hand split the pot. This article will not discuss the hi-lo version; I will only talk about Omaha hi.
Some good places to play low-limit Omaha are Party Poker or Empire Poker (they are on the same network). Another place to play is Paradise Poker but they don't have as many Omaha players.
In longhanded Omaha there really isn't any such thing as a "dominant hand" preflop. You could get two Aces and two Kings and still easily get beat. However, that isn't to say that you should call to the flop with just anything. You should still play good hands, although now there are many types of good hands, hands that become dominant after the flop hits. So, although some hands are better than others, the implied odds will have a huge effect on what hands you are playing in hyper-loose environment of low-limit Omaha.
The best starting hands in low-limit Omaha are hands where you hit two pair and your draw, for example K Q J 10. (A great flop would be Q J 3.) Those hands are a bit rare, so another good hand in a loose game would just be a hand with a lot of drawing possibilities. If you are expecting a multi-way pot, then it is important to be drawing to the nuts. In other words, you want to draw to an Ace-high flush, not a 9-high flush. Also, you don't want to draw toward straights if you have low cards and are likely to end up at the low end of the straight.
You may wish to simply call preflop with drawing hands so as to not scare away the loose-passive players. This way you also risk less if you don't hit your draw. However, if you hold a hand which has strength in high cards, such as A A K J, then you should raise. You should also raise with several drawing possibilities to build up the pot, if you feel that people are staying in too much for big pots.
Hands with only a high pair can sometimes be played. Play AAxx, KKxx definitely; with AAxx you should raise if you think you can knock people out and get the hand heads-up or 3-way. You may experiment with QQxx but that is very borderline. A set would be nice, but sets aren't so great in Omaha since someone can easily draw a flush or straight on you. With high pairs you really want to hit a high full house, and rob someone who thinks their lower full house is the high-hand. The main reason high pairs are much less valuable than in Texas Hold'em is because having an Overpair on the flop is worthless in Omaha. Most likely someone else has a two-pair.
In general, you want to fold any hand unless you have top 2 pair or a draw to the nuts or near-nuts (for example a King-high flush). These requirements can be relaxed a bit if the game is shorthanded: you can draw to slightly lower straights/flushes. However, you still don't want to be calling with one pair.
If there is a pair on board and you don't have trips, then do not draw. Most likely someone has the trips and you're unlikely to semibluff people out of the pot. If you call and hit your draw, you may be beat by a full house!
Semi-bluffs are only useful if you can think you can win outright. However, in many loose low-limit games you will get called to showdown by multiple players. In this case, you don't want to semi-bluff that much. Maybe throw in one or two for deception, but try to avoid it otherwise.
Two pair and sets are troublesome if there is a draw on board. With several people in hand, there may be so many outs against you that you will probably lose the hand! Try to go for a check-raise and punish people for drawing. However, be prepared to fold at the turn if a draw (or two!) hits and you think you are beat. If you hit your full house, you can try slowplaying (if you have the nut full house) and hope someone hits their straight or flush. However, don't overdo the slowplay, you should only do it if you really can't be hurt by the river card, and be more inclined to slowplay if the opponents fall for it often and if you have position. If you find your opponents to be call-stations then go ahead and bet on the turn anyway. If your opponents are new at Omaha and they think their Ace-flush is the nut hand when the board is paired, you don't want to slowplay. Often times these players will cap out against you on the turn and river despite the full house possibility showing!
However, please note that full house is not even guaranteed to be high-hand. It is quite common to see one full house beat by another at an Omaha game. Generally, you have a low full house if your trip is lower than the board pair, and you are probably safe to win if your trip is higher than the board pair. The best way to tell if your full house is the best hand is by paying attention to your opponents betting sequence. With a low full house, you may consider trying to encourage a bluff by checking and calling instead of betting out, on a fraction of your hands.
If you hit your flush or straight by the turn you definitely should bet hard, and even check-raise if you are certain someone will bet (But bet outright if you have any doubt). There could easily be a set or two pair out against you and they could make their full house on the river. Make sure they don't get a free card here.
Often times the board will have no straight or flush showing and you think your two pair or set is the high hand. Then a scare card will hit on the river. If this happens, you may want to check down the river. After all, if you get check-raised, you are doubling the amount of money you have put into the hand. It depends on how many opponents are still in the hand and how they played it, but in a multi-way pot, checking is usually the right move. However, if your opponent rarely check-raises, or if he has played the hand like he had two pair, then you may consider betting.
If you are on the other side of the coin, and you hit your hand on the river, you may want to bet out instead of check-raising, because your opponent may check it down. I usually mix-up whether I bet or check-raise in that situation, depending on what I think my opponent has, but also to add deception and uncertainty. It is important to make your opponents fear the check-raise so that they are afraid to bet on the river, letting you see some showdowns more cheaply.