Yes, I took the AMC (link) last Thursday.
Did you do it last year? If I remember correctly, for the last 10 questions, for each one you
* answered correctly, you got 8 points;
* didn't answer you got 3 points; and
* answered but didn't get it correct you got 0 points.
Except this year, on the paper it just said 5 points (and didn't explain any further) so many people were unsure whether to guess the last 10 if they didn't know the answer, or just leave it blank.
For tips on these competitions...plan your time! Don't spend too long on one question. If you think you are spending too much time move on. I suppose if you wanted to revise you could just practise various problems - you can get past papers I think.