I powerwash the driveway once a year. A mix of 1 cup of bleach and 1 gallon of water, letting stand for 15 minutes, should do the trick too. (Watch out for the fumes!)
At the same time, you want to look at what's promoting the mold/mildew. If trees and bushes and fences and 'junk' are preventing airflow across the area in question, start cleaning up. This is the long term solution to the problem. If moisture isn't drained from the area in question either, obviously, this too will promote mold/mildew. Do a little at a time and you'll see wonders!