Here is a link about tank cycling. Make sure your tank is fully cycled before you add a bunch of fish. Start with hardy fish like danios. They are cheap and will usually be able to survive any ammonia spikes. Cycling should take about 4-6 weeks. It sounds like your tank is a 29 gallon tank. I would stick smaller tropical fish. In my 29 gallon, I have hatchetfish, mollies, danios, cardinals, neons, tetras, and guppies. Be aware that some fish are livebearers, and will have babies constantly.
Your first choice is what type of tank you want. People generally choose between African Cichlids, S. American Cichlids, Brackish Water fish, Goldfish, or Non-Aggresive Tropical Fish / Community Fish. Generally, you should stick to one group. Some tropical fish are semi-aggressive (many types of Barbs). While you can mix them with community fish, you have to be very careful. The same goes for Angelfish (which are Cichlids). They can be in community tanks. but you must be careful. They are also very sensitive to water conditions and stress, so you should make sure the tank is ready before you add them.
After you decide what kind of tank you want, you should create a long term plan which details the fish you want to get. Some fish require different temperatures, pH, water hardness, etc. Some need places to hide, a tall tank, or lots of plants. You want to make sure you can accomodate the types of fish you want. Either way, go into the pet store, look around, do reasearch, and take your time. Go for variety. Since you tank is relatively small, you want to make sure you maximize the tank space by buying fish that swim at different levels, have different activity levels, and are not too teritorial. Some fish love to to school, others are more solitary. Try to know as much about the fish you buy as possible.
Know that you will need to do weekly water changes (including gravel vacuuming), monthly water tests (after you cycle), and light cleaning. Be prepared for a few fish to die. It happens to the best of us. Know the common diseases to look out for, and take measures to avoid exposing the fish to stressful conditions.
Don’t buy fish that will get too big for your tank. There are some common ones that you will see at your pet store that you should not house in a 30 gallon tank. For example, the common plecostomus and pictus catfish.
As far as equipment, I would go with a HOB filter rather than a canister. They are easier to deal with, and more effective for a tank that size. They are also cheaper. A Whisper 60 filter would be sufficient. It’s quiet and easy to set up. Either way, make sure you overfilter your tank. This way you can house a greater number of fish, and your water quality will be better.
I would suggest you start with 3 Danios. Then wait a few weeks before buying more fish. Some other interesting fish are leaf fish, rainbow shark, and Honey Dwarf Gouramis. You can also look in to invertebrates and other animals like, shrimp, snails, and lobsters.
