When i setup a tank, i begin with live rock (about 1 lb/gallon) and a shallow sand bed of 1-3 inches (never have had problems with this). It's best to test the water every few weeks (test kits needed) for ammonia, nitrite and nitrate. Once these all test zero every day for a week, you can consider adding fish slowly ;) . One every few weeks is best. For new marine aquarists, I ususally recommend fewer fish load (easier to maintain).

*Big fish don't do well in small tanks. I wouldn't recommend any tang species unless you have a minimum of 75 gallons. examples of other fish that need space, usually at least 75 gallons or more as adults, are most puffers, angels, triggers, many wrasse, groupers, butterflys, and a few others. See Scott Michaels' book Marine Fishes for fish info and selection.

If this is your first tank and you plan on trying corals, try soft corals like leathers, xenia, zoanthids, button polyps etc. You'll need high intensity lighting to keep corals.

hth
andrew