Some apps are more power hungry than others and can slow your Mac to a crawl. To see which apps are eating up your system resources, use Activity Monitor.
2. Manage your startup items
It goes without saying that a clean startup helps speed up slow Mac.Go to your System Preferences > Users & Groups and then click on your username. Now click on Login Items and select a program you don’t immediately need when your Mac starts up, and click the “-” button below.
3. Turn off visual effects
Click System Preferences > Dock.
Untick the following boxes: Animate opening applications, Automatically hide and show the Dock.
Click on Minimize windows using and change Genie effect to Scale effect.