Good luck RunningJumpingHorses!
I agree with everything ashsunnyeventer and albertaeventer said.
Make sure you are orgainsed. It will make your weekend a lot less stressful!
Before an event, I like to make sure I have my horses show box in order a week in advance... that way I can go out and grab extra supplies or wash things that may have been over looked if needed.
I pack my float (horse box, trailer, lorry - whatever you call it) the night before, as I clean my gear it goes staright in. I make sure I have all my necessary boots and pads as well as rugs and feed in there.
My horse gets washed the night before and depending on my start times either plaitted the night before or at the venue. I don't know if it will help much, but I do up a list like this before the event and use this to make sure I haven't forgotten anything... This is what I used for Capel a few weeks ago. capel.jpg
I always get to the venue with minimum 2 hours to spare. It allows me to get my numbers, settle my horse and set everything up before having to start getting ready. I like to start getting ready about an hour before my times (it normally takes me about 15 mins to get me and my horse ready) and then I can do last minute checks before warm up. Depending on which horse, what class and how well they have settled, I do anywhere between an hour to 15 mins warm up. It will be a matter of finding what works better for you and your horse.
In terms of nerves, I still get nervous before classes. I am better now, but I found it helps to figure out what you are getting worked up about... eg Dressage - forgetting the test... if you know your test, you will be fine. Even if you make a mistake it isn't the end of the world. Everyone makes mistakes. :)
Show Jumping - Forgetting the course? Worst case, you get eliminated... but provided you walk the course and then before you go in take a second or two to look at the course again.. you should be fine.
XC... That can be scary, but just keep calm, don't think to yourself "oh my horse will find that frightening" as you will be subconsciously telling your horse that it is scary and you will more than likely have a problem at that jump.
Have fun! Eventing is a blast and the only one who can put pressure on you, is you... Just go out there, remember to BREATHE and enjoy a fun weekend with your horse. :)