Chromebooks are not the most powerful machines out there. In an age where no speed is ever fast enough, any lagging system will be dreaded. However, there are some things you can do to ensure that your Chromebook is running at its full speed.
We all love our extensions. Some people prefer to rock a vanilla setup, while others love to customize their Chromebook to their needs. If you have extra extensions installed outside of what OJR has put there for you, if you do not use them, uninstall them. These extensions can be poorly optimized or even designed to do tasks that your Chromebook cannot handle. Eliminating any unnecessary actions your Chromebook has to do is a great way to ensure its snappiness. The easiest way to access your extension manager is to type chrome://extensions in the URL bar at the top of a chrome tab or in the bottom left menu. From here you can click remove on anything you put there yourself, but no longer need.
Look up, can you count your tabs on one hand? If yes, you're rare. The more tabs you have open and running the more your computer has to chug to accommodate your needs. Think of how hard it is for you to pat the top of your head and rub your belly. Now you're asking your Chromebook to do all that while standing on one leg, blindfolded, sing the alphabet backward, and trying to drink water. Some tabs such as YouTube take up many more resources than a tab such as Google Docs. Prioritize your workload and close your tabs!
While you cannot withdraw either the cache or cookies, you can clear them. Cookies save data from the websites you visit and cache saves things like rendered images from websites. This data is often useful, however, you likely visit hundreds of webpages a day. All of this information adds up and can slow down your Chromebook. Clearing them prevents your Chromebook from looking through the extensive library you have built up through your Chromebook adventures. Press CTRL + SHIFT + BACKSPACE all at the same time. Make sure you're in the advanced tab and click cookies and cache. Set the time range to all time, and click clear data.