If you can, bring all you own equipment (except tanks and weights). Even if the rental equipment is good (which it may or may not be), you don't want to have to start re-learning how everything works.
Don't trust anybody to setup your equipment.
Just before you put on your BC, make sure your tank valve is all the way on, then back it off a 1/4 turn.
Just before you enter the water, look at your pressure guage, make sure the tank is full, give your BC inflator a good long squeeze, take a few breaths off your primary regulator and backup (Air-2 or Octopus) and make sure your pressure guage doesn't drop much (a pound or two is OK).
You need to do this just before you enter the water, even if you did it when the boat left the dock, since there are a lot of "helpful" boat hands who will turn things on and off and adjust things (not allways correctly or to your liking), and you might not even notice that they did anything.
Doing this makes sure that you have a full tank, and that it's turned on, that your BC is inflated so you don't sink like a stone, and that you can breathe on both your second stages.
Also, don't be afraid to take the time to make sure you're weighted properly. Being overweighted or underweighted makes everything more difficult, and will make you burn your air much faster. being underweighted will make your 3m (15') safety stop very difficult.
If the DM tells you that you have to enter the with your BC deflated or do anything special because of a significant current or other conditions you're not used to, it's probably not the right dive to be going on right after certification.
Also, as several other people have said here, if anything doesn't feel right, don't dive. This applies if you know what's wrong and especially if you don't. There's always another day and another dive. Don't let peer pressure get you in the water when you don't feel right about it.
If you read the "Accidents and Incidents" board here, you'll noce that a lot of the start off with one form or another of: "Something didn't seem right".
Other than that, relax, and enjoy!
Terry
grover:
I Just started diving, completed my PADI OW course last week, were going to cuba (Guardalavaca) in a few weeks and plan on making about ten dives there, what do i have to watch out for there? My local dive school is taking us on a few dives before our holiday, to get used to our equipment ( we bought our own and are going to take it with us to cuba.)
greetz fromm the Netherlands
grover