The biggest piece of advise you can get us to be patient. Introduce new fish to the aquarium slowly only once it has stabilized. If you have questions, ask then act. The biggest mistake first time hobbiest commit is to stock their tank with a lot of fish in a short period of time, then not knowing how much food they require, and wondering why they cannot stabilize their Nitrates and such.
Also, invest in a test kit that tests the basics (PH, Ammonia, Nitrates, GH
). I use Dr. Wellfish's test kit and have been very happy with it so far. It's not that pricy and is very revealing.