Clear your desktop:
Remove any files, folders, or infrequently used Dock icons. These convenience and organizational options slow down performance by requiring the system to constantly redrawn them on the screen.
For a minimized Dock, the only icons you need are Finder and Trash. The rest of the icons can be deleted. Some people like to keep Launchpad in their Dock for easier access to Applications.
To keep icons in your Dock opposite click on the icon and select Keep in Dock. If you use an Application all the time and want it to open whenever you restart your computer just opposite click on the icon and select Open at Login.
If you are optimizing for audio or video you would want your player and/or recording software to automatically open at Login. For desktop use this could be accounting software, CAD software or a web browser.
Applications automatically opening when the computer restarts is very important to restore function for media servers or home automation.
Close all Applications
Before applying any optimizations, make certain the only application running is Finder.
The Force Quit window will allow you to view all applications that are running.
Go into the Apple Menu, drop-down menu, and select Force Quit.
Click on and highlight an application. Press the Force Quit button in the lower right corner. Repeat until the only application shown is Finder.