Biggest tip would be show that you are happy to listen, look and learn. DON'T act as if you have something to prove.

It can be hard if you are young/new as you quite often DO have to prove yourself - the trick is not to show off, be heavy handed or over-impulsive - just do what you're asked, and ask questions even if you know the answer (only intelligent ones, not 'what's this for' whists holding a spanner.....!

Chris