If you have the traditional spinning hard drive (HDD) in your Mac, maybe you'd like to upgrade to an SSD. What a difference this makes -- all favorable. If you do install a third-party SSD, then you'll want to activate TRIM. This article explains how to do this, and why. I've done two SSD installs, and it'd not too difficult, even for a techno-klutz like me.
Also, does your Mac seem to be slowing down? This article has some tips on this as well.