RazzMaTazz had it right
My rules for smooth, fast, trouble-free operation was never very long and has gotten shorter as Android has improvéd and matured.
Now, here's what I do - and more importantly, what I don't do:
I do nothing to cache files.
I don't use cleaner, manager, optimizer or saver apps.
I don't use antivirus.
I rarely manually close apps.
I do uninstall apps this way:
Settings > Apps > Select app > Force stop > Clear cache > Clear data > Uninstall.
This helps to ensure nothing is left behind.
I do disable apps I never use.
I'm careful about what I install.
I relax and use my phone.
Well, that's about it. To summarize:
I'm careful.
I use my phone.
Oh, and I do backups.