1) Bring sunscreen and aloe...you'll be spending a LOT more time in the sun if going HP vs. LP...set up, waiting for launch, march for recovery/retrieval/search for the needle in a haystack.
2) Remember the safety rules...don't arm until the rocket is straight up and ready to fly!
3) It's VERY easy to get distracted and sidetracked while up at the pads, so before you leave go through your checklist (again if needed). Make sure the rail is locked.
4) If things are rushed, just stop and go through things again slowly or just wait and fly another day when you're better prepared.
5) If it's windy, take extra time to set the angles...better yet, watch what others do/how other rockets fly before you launch.
6) Always check and confirm your electronics settings. If it's something you haven't used in a while, do the testing all over again just in case (arming, igniters, charges, etc.). It's very helpful if you create notes for each HP rocket if setups differ.
7) I'll echo the "use a tracker" suggestion...you're going big, don't make it a big loss.
8) Remember to have fun and enjoy watching other rockets...this is supposed to be safe
and fun.
9)
Make friends, learn from others, help others.