There are lots of things you can do to improve the performance of your Mac. Here are the ones that will have the biggest impact.
The more RAM you have, the better. One reason that Macs can run slowly is because apps and processes consume lots of RAM, leaving little for the others. But RAM is expensive, and adding it after you’ve bought a Mac is becoming difficult. The next best option? Minimize how much you use. Don’t keep lots of apps running if you’re not using them, and close Safari tabs. Use Activity Monitor to identify apps that are hogging your RAM and then quit them.
Hard drive space
Also, the more storage space you have on your boot drive, the better. OS X uses it as a cache when it needs more room than is available in RAM. At the very least, keep 10% of your storage available for use. Open a Finder window and select “Show status bar” from the View menu to see how much is available. Archive documents you don’t need to access regularly and consider using an external drive for your iTunes Library. Empty your Downloads folder. Use an app like Gemini to identify and delete duplicate files.
Those files on your Desktop slow down your Mac, too. OS X draws a new window (complete with Preview) for every file on the Desktop, hogging system resources. If you have dozens of documents scattered around, they will incur a performance hit. File them, Trash them, or put them in a new folder called “Desktop Clutter”.
Spotlight and Time Machine
Spotlight and Time Machine are both terrific features, but they can cause performance issues, particularly if you backup to a network drive or allow Spotlight to index an external volume. To stop Spotlight indexing an external disk, go to the Spotlight pane in System Preferences and click on the Privacy tab. Drag the volume into the window or press “+” and select it. If Time Machine is slowing you down, you can pause a back-up while you get on with work. If it’s a regular occurrence, consider using a local external drive as a back-up destination.
Shut down/delete unused apps
Apps running in the background use resources and most apps now launch very quickly, so there’s no reason to keep them open when you’re not using them. Quit them, either by right-clicking their icon in the Dock > Quit, or hit ⌘ + ⇥ to pull up the app switcher, tab to the app and then hit ⌘ + Q . Unused apps tie up disk space, so get rid of them. Use an app like AppZapper to remove everything.
Restart your Mac regularly
Many of us (especially those who use a MacBook Pro/Air), only restart our Macs when we have a problem. It’s so much easier just to close the lid and let it sleep. But restarting your Mac clears out its cache and re-initializes hardware, and so rebooting regularly can have performance benefits. Also, modern Macs, especially those with SSD drives, boot almost as quickly as they wake from Sleep. If your Mac is running slowly, restart and see if that helps. Now resolve to restart once every few days.
Turn off visual effects
If you have an older Mac, animations (such as the way the Dock slides up and down and app icons balloon as the cursor passes over them) can affect performance, so consider switching them off. Go to System Preferences > Dock, or choose Dock from the Apple menu if you’re not on Yosemite. Uncheck the boxes marked “Magnification”, “Animate opening applications” and “Automatically hide and show the Dock”. Click on the “Minimize windows” menu and choose “Scale effect”.
Empty Safari Tabs/clear cache
Have a look at Activity Monitor’s RAM tab and you’ll see that some of the most memoryintensive processes are Safari tabs. The more you have open, the bigger the performance hit. Close the ones you’re not using – bookmark them if you think you’ll need them again. Next, open Preferences from the Safari menu and, in pre-Yosemite versions of OS X, click Reset Safari in the Safari menu and choose Remove all Website Data > Reset. In Yosemite, choose “Clear History and Website Data” from the Safari menu and pick an option from the drop-down menu.
Reduce Log in Items and Restart
Log in items are those apps and processes that automatically start when you restart or log in to your account. They’re often related to software you no longer need or use. Go to System Preferences > Users & Groups > Login Items. Click the padlock at the bottom-right of the screen to allow you to make changes, then type in your password. Click on the first login item you don’t need and click the “-” at the bottom of the window. Repeat for every log in item you don’t want. Now restart.
Keep software up to date
Out-of-date software can cause performance problems. In open apps, click on the application menu and select “Check for Updates”. Download and install them if there are any. Now, go to the App Store pane in System Preferences and check off “Automatically check for updates”, “Download newly available apps in the background” and “Install app updates”. Also, click “Show Updates”. This passes you to the App Store app where you can download them.