Use a high quality microphone. If possible, use an external microphone. Lapel microphone either a condenser or electret.
Microphones built in to camcorders are generally low quality.

Check for background sounds as they will cause problems when you come to edit as you will hear the background atmos jump on every edit
Record a short length of background sound without any dialogue to use in the editing session.

Avoid wind as there is little you can do later to repair the soundtrack

Make a list of what you wish to convey in your video and shoot as much as possible a good ratio is 5:1 in other words your final footage will be approximately one fifth of the footage recorded.

If there is to be commentary over scenic shots for example allow plenty of footage to cover this

If you are doing an interview with a noisy background make sure the narrator is close to the microphone

Always use headphones when recording audio. If there is a problem in the recording, such as a loss of signal, interference, hum or the narrator turns his head away from the microphone you will need to know

If possible have spare batteries for the Camcorder, as there is nothing more maddening than running out on a good performance

Use your camcorder to get a good buzz track (atmospheric soundtrack of a scene) this can be used in editing.

When editing and there is a wobbly bit with dialogue keep the soundtrack and cut in a still of the scene or a bit of live footage that makes sense. A shaking camera is terrible to watch so use a tripod as much as possible.

Try if possible to leave the music track till last as this save constant editing of the music.

Be very careful of copyright if your masterpiece is a great success and you wish to sell it.having commercial music in your production will need to be cleared for copyright so be meticulous in taking down details of tracks. Try to do this in the editor so that the information is not lost in your project

Avoid zooms as much as possible. Too many zooms ruin videos

Don’t be afraid to ask an actor to do the scene again if you feel he or she could do better. Very often the 2nd take is the best