I use two methods
The reflective stuff mentioned above works great and can be used on side windows as well. Easy to work with cuts with sissors, really helps with insulation as well.
When parked where we don't have to deal with direct sun and want to see out we use garden shade cloth from wally world, the small command performance hooks works to secure it to the inside of the windshield. This eases daytime glare and you can still pull the shades for nighttime privacy.
We are full time and other than 3 months in Yuma we move a lot.
Jim
2007 Keystone Challenger 5th wheel, Ford F350 Super Duty 6.7L Diesel, Short Bed, 2 dogs and the cat and rolling down the road full time since May 2014