1. Reduce the number of apps that launch when you boot up.
If you have a bunch of different programs set to launch when you turn on your Mac, it's going to take a while for your Mac to boot up. You can see exactly which apps are programmed to launch on start by clicking the Apple icon and navigating to System Preferences > Users and Groups >Login Items. In this list, you'll see all the items that start up with your Mac. Check the boxes next to each app and click the minus button at the bottom of the window to remove them.
2. Check for software updates.
Often, software updates fix bugs and glitches that could be slowing your Mac down. Check for any software updates that may be available for the version of OS X your Mac is running on by clicking the Apple icon and navigating to System Preferences > Software Update. In most cases, your Mac will probably issue a desktop notification to alert you when an update is available.
3. Try restarting your Macbook.
It sounds obvious, but sometimes your Mac just needs a good restart to get back up to speed. Try restarting your Mac before jumping ahead to other options, and remember to save all your work before restarting. I recommend restarting your Mac at least twice a week.
4. Close unused tabs in your browser.
Open tabs in browsers do take up memory, even if it is a small amount. This can build up if you're the type of person who opens, say, 15 tabs on a daily basis and never closes them. Try to get into the habit of closing out tabs once you're finished using them.
5. The same goes for apps.
Apps, like tabs in web browsers, can also eat away at your memory if you have a ton of programs open. It's best practice to close out apps once you're finished using them.
6. Organise your desktop.
For some, this is a daunting task, but you may be surprised to learn that it can actually give your Mac a little performance boost. OS X treats each desktop item like a small window with its own memory footprint. So try reducing the number of icons on your desktop by combining similar items into folders and deleting items you don't use. Or, you can use stacks by clicking the desktop, then choose View > Use Stacks.
7. Delete apps you don't use.
Again — apps can chip away at your system's memory. If you downloaded a game, app, or program that you no longer use, get rid of it to free up some space.
8. Clear your browser cache.
If you mostly notice sluggish performance while you're surfing the web, it could be your web browser that's the problem, not your Mac. Try emptying the cache to speed up performance. The directions are slightly different for each browser, but in general you want to navigate to the Settings menu and head over to the History option.
9. Keep your Mac cool.
Especially in the summertime, heat can be an issue for laptops. Make sure you aren't interrupting the airflow of your fan, and be aware if you are running programs that require heavy lifting in a hot environment.
10. Make sure you aren't running too many browser extensions or plugins.
Your web browser can get cluttered the same way your Mac can. It's easy to install browser extensions and then forget they are there. You can sometimes speed up your performance by just uninstalling all those old extensions or plugins that you don't use any more. Especially if you are using Chrome, don't let it get too bloated.