Turn off the PS4 (not rest mode)
Power it back up by holding the power button on the console (not the controller)
You'll hear 2 beeps (this means you're in safe mode)
Connect the controller to the console with the USB cord
Scroll down the menu and select rebuild database
It's basically a defrag for your PS4. It'll also remove any corrupt files, if there are any. Depending on how bad your system is it could take a while. (Mine took about 10-15 min the first time I did it.) It will reset your menu items, so you'll have to pull any apps out of the library that you use. But other than that it should stabilize and speed up your system a bit.