The most important point, one which cannot be overstressed: GET AN EXPERIENCED PILOT! Here's what one beginner had to say:
I just started doing RC planes myself. In fact, yesterday I flew my plane for the first time (with an instructor). He took off for me, got the plane at a real high altitude and then gave me the controls. I did OK (in my opinion) but did have to give him the controls twice in order to get the plane into stable flight again. I figured the controls would be sensitive but I did not realize HOW SENSITIVE. I only had to move them about 1/8 of an inch to turn. There is no way I could have landed the thing without crashing.
By the way I am a full scale pilot. That did not help me at all. In fact I think it hurt. I didn't realize how much I use the "feel of the plane" when flying a real one. Obviously you have no feel whatsoever with RC planes.
You probably won't have any really bad (i.e. irreparable) crashes. (Of course, you'll still crash.) Also make sure you have your instructor check your plane thoroughly before the first flight, as someone said, "it is much better to go home with no flights and one airplane than go home with one half a flight and many little pieces." This is really, REALLY important.

Pre-flight Checklist
When your model is ready to fly, make sure it is thoroughly checked over by someone who has done a lot of building and flying. When I say thoroughly, I don't mean just picking it up and checking the balance and thumping the tires a few times. Every detail of setup and connection should be gone over in detail. If your instructor doesn't want to spend this much time checking your plane, find a new instructor.
The importance of this pre-flight check cannot be overemphasized! Many planes are lost due to a simple oversight that could have been caught by a pre-flight!
Here's a checklist:

Before the first flight:

• Weight
  is the model too heavy?



• Balance
  Is the center of gravity (fore and aft) within the range shown on the plans?
  Is the model balanced side to side? (right and left wings of equal weight)
  Are all flying surfaces at the proper angle relative to each other?
  Are there any twists in the wings? (other than designed-in washin or washout)



• Control surfaces
  Are they all securely attached? (i.e. hinges glued, not just pushed in)
  Are the control throws in the proper direction and amount? (usually indicated in the plans)



• Control linkage
  Have all linkages been checked to make sure they are secure?
  Are all snap-links closed?
  Have snap-links been used on the servo end? (They are more likely to come loose when used on the servo)
  Have all screws been attached to servo horns?



• Engine and fuel (if applicable)
  Has the engine been thoroughly tested?
  Are all engine screws tight?
  Has the engine been run up at full throttle with the plane's nose straight up in the air? (To make sure it won't stall when full power is applied on climbout)
  Is the fuel tank level with the flying attitude of the plane?
  Is the carburetor at the same height (not above) as the fuel tank?
  Is the fuel tank klunk in the proper position and moving freely?
  


• Radio
  Has a full range check been performed?
  Has the flight pack charge been checked with a voltmeter?
  Have the receiver and battery been protected from vibration and shock?
  Is the receiver's antenna fully extended and not placed within a fuselage with any sort of metallic covering?
  



 

• After repair:
  The checklist should be gone through again, with particular attention to the areas that were worked on or repaired.



• Before EVERY flight:
  Start the engine (if applicable) and test the entire throttle range. Run it at full throttle with its nose in the air for 15 seconds or so.
  Check the receiver flight pack with a voltmeter to ensure enough charge.
  Check the control throw direction for all surfaces. It's very easy to do a repair or radio adjustment and forget to switch these.