1. make sure your powerheads are fully submerged under water, no bubbles, they will work more efficiently trust me. second, make sure that there are no dead spot and that water is flowing in every corner of your tank. adjust your power heads accordingly.
2. you can buy a test kit from a local fish store like a Petco. it will have everything in there that you need to test (make sure it is for saltwater). if your levels are to high you should do a water change. it all depends on what is low and what isnt.. the test kit will tell you what your levels should be at.
3. Im assuming you have the tank where you want it and its ready to be filled with water. put your live sand in and live rock and add water to the tank (rock and sand can go in right away). turn all the power heads on and the filter and let it run for about a month (NO JOKE). this will allow your tank to mature and settle in. always test the water throughout this month and make sure the parameters are what the manual says it should be. after a month add a damsel or two and if they live for 2-3 weeks you can start planning on adding the fish you really want.
4. the type of fish that are good for beginners are damsels, triggers, clownfish, basslets. these types are hardy, but that does not mean they are reef safe and may eat corals or invertebrates such as snails.
matt i want to give you a little extra advice because i was were you are once. TAKE YOUR TIME! when i say a month i mean it, if not longer. its true, the more you take your time the better off your tank will be. fight back the urge to buy a fish and just let everything settle in, it will save you time and a lot of dead fish and coral. trust me