At the beginning of a tape, record about 10 seconds with the lens cap on before you film anything.

Try not to leave gaps between recorded sections of the tape. The camera records 'timecode' which helps you know where you are on the tape. Gaps in the timecode can confuse you or stop your editing programme from working properly.
When you've finished recording on a tape, label it, move the tab that stops you recording on it, and keep it somewhere safe.