If you are having a hard time seeing your iPad screen in the sunlight, the first thing to do is make sure your brightness is set to display brightly. To do this, open the iPad's SETTINGS APP and go to WALLPAPERS & BRIGHTNESS. Adjust the BRIGHTNESS SLIDER to FULL BRIGHT (Right Side).
Next, open ForeFlight and go to MORE and SETTING and make sure the brightness slider at the top is set to FULL BRIGHT (to the right).
To further reduce glare, there are a lot of products available in the marketplace. Sporty's has a good selection of items. Here are just a few:
Also, a company called MyGoFlight makes a tempered glass screen overlay called ArmorGlass that is supposed to work well. You can learn more here: