Sound
Unless you have an external microphone you will be using the camera mic to record the sound for your film. Sound is the biggest problem for filmmakers because it is easy to forget but one of the hardest things to fix if it goes wrong. The big tip with sound is to get rid of any other sound apart from the one you want to record. For example, if you want record dialogue make sure you are not recording it in a room where lots of other people are talking