Upgrade to an SSD
The single biggest improvement you can make to an old MacBook is to upgrade its traditional spinning hard drive to a solid-state drive. You’ll be shocked at the huge impact it has on performance.
Reduce log-in items
If your Mac is slow to boot up, the problem may be that there are too many applications to open at startup. It’s likely you never set them to launch at startup — they launch by default. Go to System Preferences > Users & Groups and then click on the Login Items tab to see a list of the apps that open when you boot your Mac. Highlight the apps you don’t want to open at startup and click the minus-sign button below the list of apps.
Reclaim space from crowded hard drive
With a hard drive near full capacity, any computer will begin to slow down. To see how much space you have left on your Mac’s drive, click on the Apple button in the upper-left corner and click About This Mac. Next, click on the Storage tab to view how much free space remains.
When you install an app on your Mac, the piece of software arrives as part of a package of files, including permissions that tell OS X which users can do what things with specific files. Over time, these permissions can get changed, resulting in your Mac slowing down. Repairing these disk permissions, in the most basic terms, amounts to reshuffling and re-dealing these permissions so that they return to their rightful place. To address this, OS X has a built-in tool called Disk Utility that does just the trick.
Open Disk Utility, select your hard drive from the left panel, click the First Aid button and then click Run to repair your hard drive.
Get better battery life
Powering your MacBook’s display is the battery’s biggest job. If you lower the brightness level, you’ll get longer battery life. Open System Preferences and click Display. On the Display tab, you’ll see a slider for Brightness. Lower it to a point between super bright and depressingly dull.
There is another display-related setting on the Energy Saver area of System Preferences. Check the box for Slightly dim the display while on battery power. Keeping your display running while your laptop sits unattended is a needless waste of battery resources. On the Energy Saver page, you can set times for Computer Sleep and Display Sleep, both of which spring into action if your MacBook sits idle for a period of time. Set as short a time as you’re comfortable with for the Battery tab; it’s less important for the Power Adapter tab.