Common 30 gallon fish include dwarf angels, clownfish, fairy wrasses (and other small wrasse), gobies, blennies, cardinals, and a few others. A 30g is right on the limit of what is considered a "nano" tank. Do you have lights for the tank at all? The first step is to get some LR curing/cycling in there and it does need some light to survive. You can get away with regular flourescent lighting when there's only LR and fish in there. When you want to keep corals you'll need more high-powered lighting. Corals should only go in after at least a month so if you dont have good lighting yet you have some time to decide.
What you will need at this point though are powerheads, LR, sand, and at least in a couple months a heater

. You will want a total of 20x turnover in the tank in powerheads so 600GPH total. Probably best accomplished in your case by two ~300GPH powerheads. Seio and Tunze are by far the best quality pumps and use the least amount of energy. Maxijets are very cheap, reliable, yet consume a lot of energy. Longterm over the course of a year or two it pays in electrical savings to get the higher-priced pumps. Powerheads are necessary to deliver Oxygen to bacteria on live rock, fish, and most importantly corals. Because saltwater is so saturated with ionic minerals it carries less O2 than fresh so more water movement to facilitate diffusion is very necessary. If, heaven forbid, your power ever goes out for more than a couple hours it is of utmost importance to get water flow back first. Lights, heaters, and other accessories are nowhere near as necessary as sufficient flow
So once you have your powerheads purchased and selected, go to your LFS and buy some aragonite based sand (20lbs will probably be more than you'll need) and around 30lbs of LRNot all LFS' sell refractometers and if yours doesnt or sells it at an outrageous price, check online

. Most hardware goods can be found near warehouse cost online and you can save LOTS of $$ that way.
Anyway, the procedure once you get all those items is to bring them home to where you allready have mixed salt water of proper specific gravity ready in buckets or rubbermaid bins waiting. Stack the LR on the bottom glass into an aquascape you like the looks of. If needed, secure rocks to each other with super glue gel. Then pour sand in around the base of the rocks to create your sand bed. Its important that the rocks rest on the glass so that they do not settle and topple your rockwork on your priceless corals. Once the sand is laid (~1-2" deep) pour in some water slowly over the rocks to fill up the tank. Turn your powerheads and lights on and wait.
The water will be VERY cloudy initially and will settle in a few hours to one day. There will be some dieoff on the rock that will fuel a mini cycle. Ammonia and/or nitrites should be present within a day or two and USUALLY within a week they will drop back to zero and nitrates will rise to 20-30ppm. At this point brown diatom algae will begin to bloom and you add cleanup crew to munch on them. Once the crew is well acclimated, consider your first fish or two. And then once the tank is a month old, consider your first corals
