+1 to what Kraigwy said.
The CMP match I was in 2 weeks ago was not who could shoot the best,so much as it was for everybody to have a good time.I am 42 years old and one of the youngest there.Its mostly for comeradery more than anything.You see some ribbing going on and some "got ya this time" antics but it is for fun.
The only advice I can give you is get a good sling that you can use in the prone positions to help steady your aim.Can't use it in the standing slow fire part.I shot a 229 1-X without a sling in the miltary bolt class and that was better than some who had them.I got an original issue sling for my Mauser K98k last week and just practicing at home can see a huge difference in how steady I am.
Several of the best shooters have 100/100 scores in both the slow and rapid fire prone segments.Its the standing segment that everyone falls off on so practice on that.
Be sure that you have 3 or 4 clips with you also.Don't get discuragged if you are not the best right off some of these old fellas can really shoot.I had one of them tell me "hell son I can barely see the target anymore" at the rifle clinic in August.He then shot something like a 100 6-X in the slow fire prone position.Everyone there at both the clinic and the meet were very helpful and willing to give good advice,no learn it yourself mentalities at all.
I for one was looking for something to do that I would not be put down because I didn't know what I was doing and this fits the bill.I have always been more comfortable around older folks and these people are good old fashioned down to earth people that are just out to have a good time.
If you are looking to get into serious competion this will at least get your feet wet and give you some idea of how a match is conducted.Be safe and have fun!Russ