The swim part is the bugger of it. As long as you don't have an old school NAUI instructors who make you breat off the tanks without an regulators or anything...lol Kidding.
You will be exposed to a little bit of rescue and navigation work that might stress you a little.
You also learn snorkling.
The dive tables and what not is probably the most mentaly demanding...
If your using a dive computer though it superceids your manual tables but you'll need you manual tables as your backup.
Normally the paper tests are open book so take your time and work it thought... You don't have to ace the test.
Above all else stay relaxed and use your head. Under NAUI, even if you ace all the tests and swimming requirments but you look prone to panic or be a hazard to your self and others in the water, they don't have to and might not pass you.
When you do your mask flood and removals... point your nose DOWN not UP. Keep a little positive pressure on your nose (not blowing out though) and open the TOP of the mask to slowly flood the mask (you can partial flood like this to clear a mask of fog too). If you look up and lift the bottom you'll get a nice shot of water up your nose as water rushes UP to fill the mask.
Keep looking down a little, Then when you put the mask back on (and clear your hair from the skirt seal) , look up, apply a light finger push against the top glass rim on the mask, and and SLOWLY exhale out your nose. The water will exit the bottom of the mask as the air pushes it out.
If you feel you need to pactice ANY of the the skills they show you more, ask the instructor to repeat them with you until your happy with it. Don't just slop through and not learn it correctly.
The more relaxed you are the less air you'll burn though. A little stress in the water will have you sucking your tank down at an alarming rate and wondering why everyone else has so much air and your calling the dive over early for your buddies.
DO NOT pop to the surface in a panic if something doesn't go right, get your air in your mouth, take a breath or two, calm yourself, and figure out what to do at the bottom of the pool. It goes a long way later. You might even impress you instructor by being a calm cool and collected diver.
If you have more air you might get to practice more skills while your classmates are busy breaking down their equipment after the dive... more fun pool time for you.
Oh... PS: The BC inflator valve isn't an elevator button... Swim up not waste your air to start upward motion. Once you start up the air in the BC expands and you'll be venting it anyhow... don't waste more breathable air just to start floating up. The less air you use in your BC the more you have to spare.
Keep looking around here, there are a lot of good tips on the scuba board that will go a long way in making you a better diver that a class doesn't have time to teach you.