Just to echo the other divers, going single (and I’ve had to do it every time since my friends don’t dive) is actually one of the best things I’ve experienced with diving. It’s a great opportunity to meet new friends and pick up additional tips and techniques. So relax and enjoy!
I stress "relax." When you relax, you can think. We once dove with someone who was so nervous with her bouyancy that she kept hitting the wrong button which sent her shooting up to the surface. I rent a lot, so I always do a touch test of my inflator, dump valve, weight release etc so I know where they are and how they feel before I get in the water.
Another thing to remember just because I’ve seen it happen: if you are diving with a weight belt instead of integrated, cinch that weight belt tight before each time you hit the water. Remember, as you descend, the pressure compresses you so the weight belt will seem looser. I’ve watched a diver lose her weight belt while descending. She couldn’t descend because she was too light and other divers had to rescue her weights.
Other than that, everyone else seemed to cover the rest of the highlights. Have a great time! I am envious.