Proper methods for cleaning window sill
Cleaning them:


If I have good access from outside I push up screen (or remove), close window and hit it with a hose or power washer - from a decent distance.
Open window and get everything wet.  Soap and hot water.  With one paper towel you can take away 90% of the dirt on one window.
Use old toothbrush, old butter knife, and a washcloth on the rest.  
Dry them with a clean rag.
Apply a marine wax (here is a brand I have used with good results).  By waxing it you are not ridding yourself of window cleaning.  However I have found that a lot less stuff will stick to your window sill/track in the short term (6 months).  


Aside from shuttering up your windows, you will always get dirt in thise area.