In PLO you get dealt four cards instead of two. You must use two cards from the ones you are dealt, and you must use exactly three of the community cards (flop, turn and river) to make up a standard five-card poker hand. This differs from No Limit Texas Hold'em, where you can play zero cards from your hand if you wish (known as 'playing the board') or even just one. For example, if you have the Ace of hearts and there are four hearts on the board then in Texas Hold'em poker you have the nut flush. In PLO you would not have the nut flush unless you had a second heart in your hand to go along with the Ace of hearts. Make sure to remember that you must always use two cards and two cards only from your holding and you will avoid silly errors like this!
So what makes up a good PLO poker hand? Just like in Hold'em the best hand to pick up is pocket Aces. However, in PLO, there are what you call good Aces and bad Aces. A hand like Ac-As-2d-7h is strong but it also has many limitations. Because you don't have two suited cards you won't be able to make a flush and it will be very difficult to hit a straight too. Compare this with a hand like Ad-Ah-Kh-Qd. Now you not only have the biggest pair possible but you also have tons of straight and flush possibilities that will give you a much bigger chance of winning the hand. While any Aces are technically going to be the best hand pre-flop it's important not to get carried away after the flop if they do not improve. Aces can be outdrawn much easier in PLO than in Texas Hold'em and that is why it's important to have back-up in the form of a connected Aces hand like Ad-Ah-Kh-Qd. If you think your Aces are behind after the flop you can't be afraid to throw them away when playing PLO – it's just a natural part of the game.
Looking beyond Aces, the main thing you are looking for in a good PLO hand is connectivity. Do your four cards work together? It's much better to have a hand like 9h-8h-7c-6c, where all four cards help each other out, than a hand like Ac-Kc-5h-6h. In this case, you really have two completely separate hands. Yes, they're both playable hands but to think along these lines is too similar to Texas Hold'em strategy. In PLO 9h-8h-7c-6c would be far more effective because the chances of hitting a huge draw, two pair, a straight or a flush are far higher. Try to focus on hands like this and don't be seduced by hands that include one or two completely unrelated cards, such as Ac-Qc-Jh-3d. Just that one irrelevant card (3c in this example) severely handicaps the power of your hand.
One final thing to remember when you first start playing PLO is that it takes a much stronger hand to win at showdown than it typically will in No Limit Hold'em. As there are so many more cards out there in players' hands there is much more chance of hitting something big. As such, you generally want to be drawing to the nuts at all times and to have something close to the nuts before you commit to playing a huge pot. This is different to Hold'em where any flush would usually be considered a good hand. In PLO, a six-high flush is going to be hugely vulnerable to losing against a bigger flush. Don't let this allow you to play scared – opponents won't always have the nuts! – but do have it in the back of your mind. If a player is being really aggressive and you don't have the nuts there is a decent chance he will!