1. Enjoy it!

Be prepared for subtle differences - it's hard to describe them (apart from the obvious ones such as noise and vibration, and the control loads). Try and get into the habit of using the rudder (on most light aircraft i've flown its easy to forget it exists!).

Do as much hands on as your instructor allows...

Hope it goes well!

Charlie

As said: have fun, but FOCUS! This is harder than it sounds.

Very important: Make sure your seat is in the right position. Your arms should be bend (hands aboce knees) when touching the controlls or you'll wind up begging your instructor to take over again after 15 minutes or so. 

Also: Don't nod your head when answering. Say YES or NO or whatever else is required. Look for other planes and tell your instructor when you see one close to you or will be in the near future. (example: traffic, 2 'o clock low)
This way he/she knows that you're paying attention to the outside world as well. And don't hasitate to correct your instructor when he does something wrong. He/ she can do it on purpose to see if you're paying attention. (Mine turned the compass in the wrong way, that sort of stuff)

As for the FS/real difference. It's just handy to know what all the gauges do and it's nice to know something about traffic patterns and how you controll the aircraft. Your instructor will tell you anyway.
As for the flying itself: All your FS experience means exactly d*ck when you're going to fly a real plane. It's very different. My big mistake was looking at the gauges all the time, instead of trying to 'feel' what the plane was doing.

Anyway, you're going to have a very good time and I hope this helped prepare you a bit.

Oh... and try not to squeeze the controlls. You can fly a plane with 2 fingers. (Don't really fly with 2 finger though! unless your instructor tells you to) Try to be relaxed. Let the plane do her little dances. It all doesn't matter as long as you get where you're going. Try not to gain/loose too much altitude though. Flying a plane is more like sailing a boat than driving a car. Good luck, and have fun!

Hmm... here's a few lessons learned:
Don't be intimidated or discouraged if the CFI seems to be throwing a lot of info. at you- that's typical, and if the CFI is good, he or she will also make sure you are learning what you need to know to get started and have fun. They aren't out to spoil your fun- they just want to see how well you soak this stuff up, esp. if you have told them you're serious about learning to fly. You'll be allowed to forget some of it later, but not for long...
Be sure to acknowledge what you're being told (like if they say: "my airplane". Instructors like to know you intend to let go when they ask you to), and by all means speak up if it is unclear or you have some question about something the CFI hasn't mentioned. Feel free to criticise, also- you're paying for this. Their response may teach you something important (like that you don't know what you're talking about, or perhaps that this is somebody you won't be happy flying with), or you may remind them that they're still learning, too. Just save your critique  for the de-brief   , and think before you speak. My CFI for my 2-year review surprised me recently by asking me "How did I do?"- the mark of a good instructor!
  It's easy to sort of fall into a trance the first time you grab yourself a handful of airplane- savor that moment, but remember, it's a flight lesson, and you should make the most of it. Daydreaming or fooling around is for when you're on the ground- real flight is like walking the razor edge between total abandon and the most intense, serious concentration... I love that edge, and I think you might feel at home there, too.
  And if you're disappointed afterwards, feeling you could've done better, get over it- just turn that around and decide to fix whatever's wrong next time. And if the instructor rubs you the wrong way (liike if they yell at you or whatever), don't be shy about choosing a different one for your next lesson. Don't mean to be negative- it happens...and the instructor-student relationship must be harmonious, or your training will suffer.

As for the differences: no matter how good the FS model, it's not quite the same, handling-wise... and it's also very different when it's a dual lesson.  But I bet you'll find that in many ways, flying a real 152 is easier than in the sim, depending on weather conditions that day.
Good luck, and let us know how much fun you had!!

Ooh yeah- seat postion; that's a biggie. Take some time with that before start-up. Depends on the plane, but you should be able to at least crank the seat higher or lower as well as setting its fore/aft postion. The 172s also have a crank under the seat to adjust the angle of the seat back, but i can't remember what the setup is on 152s...
Whatever the case, it's important to have things set up right for you. ask the CFI, BEFORE STARTUP, how to adjust it and what he/she thinks is right for you. Personally, I like to be just high enough to see a little sliver of cowling over the panel and glareshield... any higher in a high-wing and you can't see well out the sides. As for your distance from the panel and controls: experiment. And make sure the seat is latched on its rail   before takeoff... !!  I've had old 150 seats slide back a few inches on me... a little too exciting!

Well, I'm glad you had fun. Keep at it, because learning to fly is a very rewarding experience.

Nice to see you enjoyed it! Good luck on your future lessons (and career?).

Cheers for all your help everybody!