What are some tricks I can teach my guinea pig, how can I teach him, and how long will it take? PLEASE answer!

GPs are stubboren and do things they want to so it'd take work but it's possible. An easy trick to learn would be come. Just say it's name when holding it and put it down then give it a treat. Eventually, put it down and say it's name. If it comes, give it a treat. If it doesn't, call it again. Never punish your GP though.

I know that some people have taught their GP to do a circle and stand.

There are vids on youtube of guinea pigs doing the circle trick

http://www.youtube.com/watch?v=-LrTtWjOSwI

Hehe..of course food is involved.