Here's a link to a guy flying pattern and explaining things on a sim:

http://www.nsrca.org/d7/practice.htm

It's true what was said above about flying in a straight line - it's probably the hardest part, and if your lines are not straight and your plane is not level, your maneuvers will look like manures.

To start practicing for pattern, you should start practicing flying in a straight line, a set distance (100m) in front of you, and fly parallel to the landing strip. Do a simple move, like a 1/2 cuban 8, and fly back at the same altitude, the same distance, and just as level.