I use Clorox "Clean-UP" Spray it on, use brush on a long handle,rinse and it looks like brand new. I always make sure the awning and slide covers are dry before retracing. I I have to leave a campground with wet or damp awnings, I make sure I let them dry out in the sun before short term or winter storage.
We use Tilex for ours. We mix one bottle of Tilex along with another bottle full of water and mix it in a pressurized spray bottle (insecticide ones).We have one designated for the awning. We pretty much saturate the awning with the mixture and then roll it up for about 1/2 hour. We open it up again and then rinse. Most stains are gone and then just use a ladder and sponge for the tough parts. Doesn't require a lot of elbow grease and pretty effecient.