First off, don't be worried. The fact that you are hired and in the door means that they already think you have made a good impression and have the capabilities they are looking for. Second, good for you. The fact that you are nervous means you want to do a great job and exceed expectations as well as grow in your fiend. Nothing wrong with that unless you can't sleep and show up your first day comatose. Here are a few short tips I would suggest:
1. Don't be nervous, you already got the job
2. Listen, Listen and Listen some more
3. Take lots of notes and try and learn everything about everything... think of this as a 90 day sprint to getting to know everything.
I would also suggest you go look at the following links..they provide some useful content that you would find helpful.... Good luck and keep us posted, or ask other questions you might have.
Common job issues and solutions
Focus on These Things to Succeed
New Employee Resource Center