Q: What is the best way to speed up my older MAC?

Hello;

There is really no answer to your question.  Speed is relative and depends on many factors.  Your "older Mac" may be running as fast as it can.

Barry

Is it slower than it used to be?

Determine if insufficient memory is limiting performance: Using Activity Monitor to read System Memory and determine how much RAM is being used

Install more memory: iMac: How to remove or install memory