Don't grab a rag and wipe them.! first mistake,,, all you do is smear the screen with whatever is already on there,!
What i like to do, is
Make sure its clean to start with,, as kity said a clean screen makes a big diff.
Don't drive with the window open, it's not going to help,, just going to let more damp air inside.
Turn the AC on,,, and the heater, DRY air is what you need to keep it clear,,
Once clear, turn the heat down and find the comfort level whilst running with the AC on
Works for me
BHG