Or, your game won't load for one reason or other. Try these basic steps!
If PPSSPP won't start at all, scroll down to that section below.
Just run the ISO file directly in PPSSPP, do not extract it into files.
Some games can actually work when played from a folder when extracted, which can be useful if you're dabbling in game modifications, but many require a specific disc layout, and will not work this way. You have to run the ISO file directly.
In PPSSPP, you can right-click (or long-press) the game icon, and on the screen that pops up, press "Calculate CRC". From PPSSPP 1.16 and later, it will tell you if your ISO file is known to be valid with a little green notice.
If not, it might still be a valid file, but it's worth looking into (re-dumping it from UMD, for example).
Settings like "Skip buffer effects" can completely break graphics in some games. Do not use them.
If not, there might be something wrong with your graphics driver, and it might be worth trying another rendering backend in settings.
Place it in the PSP/GAME directory in your memstick folder, don't try to run it from elsewhere, it might not find its data files.
Try these steps in order, one at a time:
Not much you can do! Just make sure you're on the latest version using Google Play's update functionality.