Picking up a good book would be a great place to start. That way you will have all the needed info right there in front of you. I would saltwater aquariums for dummies, but there are many otheres.
Ok, here are a few things that might help you start out.
The bigger the tank you can get, the better. You have a 30gl thats fine, but you are limeted to what fish you can have in there. Over time you could have about four small fish in there happily. Thats just a rough estimate. The rule for starting out a tank for size is, an inch of fish per five gallons. The longer the tank has been running the less the gallons. So say after about six months of you tank up and running with a fish or two, you could go to an inch of fish per two gallons. Now the inches of fish are when the fish are full grown.
Good filtration is important and so is lighting, especially if you plan of having a reef tank. Saltwater fish require special foods, and water conditions, so look into that.
A sand based substrate for the botton of the tank is better than crushed correl, the finer it is the better. It helps to have it small so that crabs and snails can clean the sand bed for you, so you don't have to.
There is sooooo much to this hobby. I can't possibly explain everything that you need. Get a book, read all of it, and then if you have any other questions, come and ask us. Oh yeah, don't always listen to what your local fish store has to say, they don't always know what they are talking about. I learned that the hard way.