go to home depot and ask for graphite powder (like
this) and puff it into the rubber gasket on the door that the window slides up into when you close the window. Obviously start at the bottom. Just a little puff is all you need to do.
My car is going on 13 years of age and the window motor still works...do NOT spend money replacing it.
I've done this two or three times over the years.
I think it's mainly due to the humidity, the rubber sticks to the window and makes it hard enough that it can't go up.