My two cents, for whatever they're worth.
I agree with everything said so far, and want to reinforce the comments on listening. The last thing a clinician wants to hear from you is "Yea, but...". If they tell you something that is different than what your local association tells you, just file it away in your mind, but don't argue back. Also, Chuck's comments about talking to clinicians outside of your court time are good, and they can be very helpful, but be careful. Don't talk to clinicians after your game, for example, while they're supposed to be watching that next game. And don't monopolize their time after hours. It's good to ask questions, but I've seen well-meaning first-timers corner a clinician and talk to him for a long time about various off-the-wall stuff (like what happens if a team is up by 135 points, and there's only one player left because everyone else fouled out..
Be approachable, be friendly, ask appropriate questions, but don't be over-bearing.
The shorts vs. pants question is interesting as well. If this is your first camp, and you're going to learn, wear what is recommended and what everyone else is supposed to wear. If it's an evaluation camp, I've seen it work both ways. In other words, most summer evaluation camps I've been to recommend shorts. But there have been times a few people wear pants, and it has helped them because it makes them "stand out" a little from the crowd and it looks a little sharper than shorts. I have also seen it work against people as well, because I have heard comments such as, "Whay are you wearing pants? Apparently you can't follow instructions - the camp brochure said wear shorts." Some assigners might also be using the shorts to see if a ref has had knee problems in the past (scars, etc.). So use with caution, but err on the safe side by wearing what's recommended.
Above all else - learn and HAVE FUN! Meeting fellow refs is the best part for me.