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.