4. Create a new project, and import your old project into it.
5. Make sure the "Essential Graphics" panel is closed when unneeded.
6. Make sure you keep your number of open timelines to a minimum.
7. Transcode all MP4 footage to ProRes.
8. Do not keep a waveform (sound file) open in the Souce Monitor while you edit. (I don't know if others have this issue but it is definitely a bug on my machine, on a brand new Mac Pro 2019 tower it slows my machine considerably)
9. Quit Premiere, open terminal. Type "sudo purge" enter your password, and hit enter. Wait until finished, then re-open Premiere. (As I understand it, this resets unused memory to allow it to be reallocated. Memory can be "lost" if an application crashes and the memory is not "released" back to the OS. Most say this is unneccessary but I have noticed performance improvement without necessitating a restart, and anyway, it is a harmless procedure.)
10. In the Get Info dialog box for the Premiere Pro application, select "Open in Low Resolution", re-open Premiere. (This does not seem to affect anything visually but seems to have fixed a severe lag problem for me recently on a 5K monitor).
Error or problem, Performance, User interface or workspaces