Keep them short, avoid panning (think pop video). Make sure the material is original including the background soundtrack. Shorter is better - 2 mins will get more total views than a 7 minute video clip. For best image quality use DIVx Mpeg 4 format.
Hi what o/s are you using if it is xp or vista go into your start bar and open windows movie maker (WMM) you can make your own movies with this software, heres 1 i made of my car using WMM