As said, take your time.
You will be nervous as all hell, try and pick a test & tune or street meet to go to, you'll feel a little less under pressure as it is more of a fun atmosphere, even the best of them f**k up from time to time and if so, this is the place and time to do it.
Now, onto the car.
Get as much weight out as want, I generally drop the spare, take out all the tools, clean out the centre console & glovebox, take seatcovers and floor mats out. It's free hp, all that **** adds up.
Make sure your car is serviced well and has no leaks, make sure its as clean as you can get it.
Since you haven't been out before, I'd say just go and do what feels right in the car, see what times you pull.
If you are going to change ANYTHING on your car, do one thing at a time or adjust only by a little bit.
Most importantly, just go and have fun with it.