When it's dirty, you can't get it dirty again... But when it's clean, you get to cake it up properly - makes a play day far more rewarding!
Here's what I do:
Take it to the imigrunt wash on a Saturday morning, make them sweat cleaning it, then drive round for a bit when it looks all shiny and new... Go to a play site on Sunday morning and everyone will look at you in your 'shiney' and think you're all show and no go. Then the fun begins! See how crapped up you can get it in a day.
Then, drive it to work for a few days, leaving mud in the car park when it rains - this also shows the neighbours you actually use the fecker properly. Then back to the imigrunts and make them clean it again ready for the next weekend!
Every so often I give it a really good jet wash in the drive way underneath to check it out and make sure all the stubborn muck is out of all the corners and stuff. And spend as long again cleaning the driveway out to get rid of the mud!
Giving it a good going-over yourself is always a good thing cos you can check it out properly for potential problems before they leave it out of action.