If you are familiar with Hold'em, you know that big pairs are very strong cards. In Omaha, with the exception of a pair of Aces, cards in your starting hands require a certain amount of synergy to make them worthwhile.
High pairs are playable, but expect to need to make a Full House or stronger in order win hands which go to a showdown.
3 or 4 consecutive cards will give you a better possibility to make a straight, and two cards in each of two suits (double-suited) gives you more flush chances, so these types of hands are playable if the betting is not too big. It is important to think ahead and remember that you will usually need relatively strong straights and flushes when you make them. Second nut hands in Omaha lose much more often than in Hold'em and can be very expensive.
Omaha starting hand strength depends on whether you are getting all your chips in pre-flop or just calling. If there is heavy action and you suspect other players have high pairs, a hand like 6-7-8-9 may be able to catch a good flop. Having four cards working together is very important if you are going to find yourself all-in pre-flop, or unlikely to fold whatever the flop.
Make sure to keep in mind that in the end, you can only use two of your pocket cards to make your winning hand. A third card of the same suit in your starting hand makes it less likely that the flop will include that suit. Similarly, having multiple Kings or Queens may not play well post-flop, because there are less left in the deck lowering your odds of landing another.