How to Behave at a friend's mother's Funeral?

Try to keep it simple and polite. Don't get over emotional or talk too much as it won't look genuine. If you are introduced to the father/members of the family you should show your respects by saying that you are sorry for their loss. Don't go out of your way to do this however. Just try to stay close to your friend most of the night, as your main role should probably be to support them through the event.

You just say Im sorry about the loss h

Then you put your head down and walk away too much will just get the person even more upset

just be real, don't add extras if it isn't in your heart, they can tell. Just tell him you're sorry for his loss, and move on. If you aren't really close I doubt he'll expect for you to do too much.

Good luck

Yep, you just pay your respects to the family by doing just that.

be subtle! try not to be noticed