Should you use "going to" or "will"?

Will is a more definitive term than going to. Telling your parents I will get my homework done sounds more certain than I'm going to get my homework done.

Use will for future facts, e.g. The Prime Minister will serve for four years.

Use going to for predictions based on current evidence, e.g. There's not a cloud in sight. It's going to be another warm day.