Well a couple of things I have seen do not forget to wet your straps on your bcd before putting the tank in this is the one I actually did got in the water and had a fun dive then while coming out of the water at the beach the tank started dropping out, kind of a pain in the rear.
I have almost done this next one but I have watched many do it make sure your regulator is in your mouth before descending. I have seen even experienced divers swim out and go to descend and realize opps that not my reg in my mouth.
Other than some basic safety issues remember that you are supposed to be having fun, So as hard as it may be relax and enjoy yourself. It will be much easier on you as stress tends to make everything harder.
One last piece of advice take your time descending equalizing comes easy to some and harder to others not everyone can drop like a rock to the bottom keep your health and safety as the number one priority.
Have fun!!