I have a 30 gallon reef. It is working beautifully. I have button polyps, mushrooms, star polyps, lots of inverts, 1 tomato clown, and 2 blue chromis. Here is what I did to get it started:
1. Start with the tank only. Add sand and then water with salt solution. The sand will settle after a week (before then it looks like a sandstorm that you can't see through).
2. Add a heater, protein skimmer, your filter of choice, and a couple of powerheads. Don't forget to choose PC, VHO, or MH lights if you want corals. For just fish, the lights that come with the tank are fine.
3. Add live rock. For a 30 gallon reef, you must have at least 30 pounds of LR.
4. Cycle the tank. I use pure ammonia to do this. It generates all the good bacteria without hurting any fish or stinking up the room with cocktail shrimp. My 30 gallon reef cycled completely in a week doing this. Be sure to test the water daily. Also, even if the water appears normal (cycled) one day, test daily at least a week afterwards to be sure there will be no spikes. DO NOT add additives to the water during the cycle as this can slow it down.
5. Add cleaner crew (inverts). I have a serpent star, cleaner shrimp, fighting conch, emerald crab, and tons of snails. These will keep your tank clean of debris from fish and their food, but add them before fish to reduce algae, diatoms, etc.
6. Add fish slowly. 2 clowns for a 30 is great, and I would caution on getting more than that. Maybe something small like a lawnmower blenny or firefish. BUT, definitely NOT Dory. Too small of a tank for her.
7. If you want, you can add some corals, sponges, etc. Sponges don't need special lights, but corals do...so do research on every specimen you concider.
For a tank of that size, I recommend an HOB skimmer like the CPR Bak Pak 2 or the AquaC Remora. I have the CPR, and I put the heater inside. My filter is just a cheap HOB that I use with carbon, phosphate & silicate magnets. It works rather well. I use Maxi-Jet 900 powerheads. Be sure NOT to have them spray bubbles in the tank. In FW, these bubbles are pretty, but in SW they can cause disaster with certain things such as sponges. I also used 2-3 inches of sand as substrate. Snails, conchs, other things crawl around in the sand and make your system complete.
The most important thing you need? PATIENCE. Don't ever rush a reef. It always leads to disaster. Good luck!