Whoh. Glad I saw this.
First off, start reading as much as you can, from as many different places. You will start to learn what sort of filtration system will work for you.
Secondly, buy the tank, the system sand and rock. I recommend dry sand, live sand is usually lousy, and it is not live. I use aragonite with a grain size of 1-2mm so that I can gravel vac it.
Now start looking that fish that are acceptable for a 30g aquarium. NO tang is suitable for a 30g aquarium. You can start on
www.liveaquaria.com looking at fish (this pretty well covers most of what you will see in a pet store) and from there you can start to research your stock. What do they require etc. Do not just rely on what fosters tells you, seriously go out and google them. Read about their care on as many different sites as possible. Then start coming here and telling us all what you want in your tank. We can give you personal experiences with those fishes or combinations of animals.
Now, make sure that your tank has cycled, and you can stock your clean up crew. (snails, hermits, sea stars...whatever)
After that, you can add your first fish. My usual rule of thumb is that I wait one h2o change in between fish additions. Helps your h2o stay clean and stable, and also allows your BB colony some time to grow to meet the demands.
Now after your tank is fully stocked (which should not take long in a 30g tank) you need to acheive stability.
Once your tank has matured, and all parameters are coral growth acceptable, and stable - you can start adding corals.
I would research what corals you might want to keep now. Again, start at liveaquaria to get some ideas of what stuff looks like, and then start researching the web, and checking stuff with us back here. We can make sure that you avoid, or are at least aware of bad combinations, things that will kill or eat other things, or things that ended up just dying for us or being headaches. Trust me, there is more to coral selection that just looks.
I also wouldnt tell you to just go out and add a leather coral. Leather corals once attached to the rock are almost impossible to completely remove, and they are fierce chemical competitors. In such a small tank as soon as that leather coral got comfy, it would have that tank saturated with alleopathic cometition. These specific chemicals can brown or kill sps, will kill trach brains (talk to me about this, lost two $500 down the drain) and kill other softies, corals and anemones.
Going back to the tang thing - tangs for the most part are lousy for algae control, especially the kinds that newbies are prone to getting.
I own three large tangs and I have to trim my macro algae in my tank.
In addition to that, you should never be using animals for algae control. All you are doing is making more waste, which will in turn become more algae. What you need to do is improve your h2o quality so that you dont have algae to start with.