I make my living with Pr and Ae, and it's vital I keep my system running, and not encounter any job-stopping problems. Here's my checklist of troubleshooting Pr on Mac.
I don't even post my problems here unless I've tried all these fixes first, as these routines haven't failed to get me back in business (so far), unless the problem was a bug. Those can't be fixed by us, but some can be worked around.
1. Trash Preferences (fixes most Pr problems when "it's just not working right"). Hold down Option while launching.
2. Delete media caches and previews. Do this after an application crash or hang.
3. Check for corrupt media in your project. This can cause major performance degradation, freezes and crashes. Remove or transcode problem media to some other format.
4. If Pr is simply sluggish, reboot the computer (Pr has RAM leaks), OR much faster, open the Terminal, and type in "purge" (no quote marks) and hit Return every so often. You can tell you're out of RAM when you open the Activity Monitor > System Memory tab, and there's no Free RAM left. Free RAM defaults to the green color. A lot of blue (Inactive RAM) is caused by Pr. It's RAM that's not accessible. Low RAM causes performance issues, and I'm gobsmacked that Adobe hasn't fixed this problem yet. Purging will turn the blue Inactive RAM into green Free RAM. The longer you work in Pr, the less Free RAM becomes available, and the more sluggish it will become.
5. Run Disk Warrior (esp. if you're getting beach balls, AND every time after a computer (not application) crash or freeze).
6. Re-install the application.
7. If you have an external video (BMD, AJA, etc.) or audio card that requires third-party drivers, remove them and see if the problem vanishes.
8. Re-install graphics drivers (this has fixed display issues for me, such as video not updating in real-time).
A lot of people suggest Repairing Permissions, but this is mostly useless advice. You need to do that if you're getting "directory access denied" or "can't write file" errors. However, it can't hurt. Disk access is vital to caching, previews, and project saving. If you're having permissions issues, the app will either stop working (if it can't cache or write previews), or it won't let you save your project.