In reply to tscoobydoo:
Get the face in the picture, the back of a persons head just isnt that interesting... focusing on the eyes usually works well, but might require you to find a good (safe!) place up above the climber, or diagonally up so that you aren't risking dropping stuff on them.
An uncluttered background is good, so clear away bags/hats/jackets/sandwiches/random shoes that might sneak into the shot.
Then just take lots and lots until you get a cracker!