#About every eight weeks I clean the ledges on my windows so that between the rubber seal and the ledge there is no dust or dirt.[I can't think about how to translate what I mean any better, sorry]
It keeps the rubber alive longer.

#Twice a year, in spring and in autum I grease the rubber seals on windows with Vaseline/petrolium jelly. It stops the rubber from drying out during the winter and helps keep it flexible.