something no one else mentioned was first checking to see if your car has an in-cabin air filter. if so, it might be a good idea to check and see if it needs replacement. dirt and grime can accumulate on the inside of your windshield, which will allow moisture to collect easier than if it were clean.
i guess the second practical thing you can do is keep your inside windows clean. they seem to fog up less for me.
and finally, yes, use that rainX anti-fog spray and make sure you apply it properly. i remember goofing around w/ it and trying it on my bathroom mirror, and i still have this circle that fogs up less than the rest from a year ago. good times.