My two cents:

1) Don't go out for excessively long lunch hours. People are watching you believe it or not.

2) Don't surf on internet too much. Same as above.

3) Be honest with your boss. If your boss is not in office that day, don't think he/she won't know that you leave at 3!

4) Maintain a good relationship with your prior boss and coworkers-maybe one day you need their help in finding a new job.