I believe that many friends will feel this way. When buying a Mac, because of the limited budget, all versions with small memory are bought. As time goes by, more and more software is installed on the computer, resulting in insufficient system memory and insufficient memory. Every time you want to install a software, you must uninstall some software first. In fact, you don’t need to do this! If you are in trouble due to limited storage space, you need to take these steps proactively to free up valuable storage space on your Mac. In this way, your Mac won't make you fear when the disk is almost full.
1. Empty the trash can
Did you know that macOS does not automatically clean up items in the "Trash"? There may be only a few gigabytes of data.
On the Dock, right-click the "Trash" icon and select "Empty Trash." After deleting the data, you will no longer be able to access them.
2. Uninstall apps you don’t use
If you are the kind of person who reads technical websites, you might just want to try new Mac applications and see what they are for. But it's easy to forget to delete them when you finish the test.
First, record the content on your machine. Applicable APP Uninstaller application. App Uninstaller is an uninstall application that comes with Mac, it will automatically delete all junk files related to the application. 
If you are using macOS Sierra and later, you will be happy to know that macOS has built-in storage management features (we will quote multiple times in this guide).
Click the Apple icon in the menu bar, select "About This Mac", and then go to the "Storage" section. From here, click "Manage". 
You will see several options. The first action you should take is to turn on the automatic emptying of the trash after 30 days.
Next is to click on the "Apps" button. You will see a list of all apps, sorted by the space they occupy. Select one or more apps you want to uninstall, then click "Remove". 
3. Find and delete large files
In the same storage management window, click the file option in the sidebar. Here, you will see a list of all files, sorted from largest to smallest.
The best way to reclaim a lot of storage space is to delete a few huge files. It takes longer to clear hundreds of small files. Look at the files at the top of the list and see if you can do without them. To delete a file, click on it and press the "Delete" button.
If you have space in your cloud disk account, you can move files to cloud storage to free up local storage space.
Once the large file is gone, it's time to continue down to view the others. A 1.5GB folder is filled with photos you don't need, it takes up as much space as a 1.5GB video, but it is difficult to find.
macOS makes this easier. At the top of the "Documents" view, you will see two other options for sorting files: download and file browser.
The "Download" section provides you with a breakdown of files and folders older than three months, six months or one year. So you can browse files that have not been visited for a long time and decide whether to delete them.
The file browser part is basically a lookup view in the storage management tool. You can browse the entire file storage system and find the file or folder you want to delete.
4. Delete iTunes files and iOS backups
If you back up your iPhone or iPad to a Mac, the backup may take up billions of bytes of storage space. In the storage management window, click the iOS Files section. Once you are sure you want to delete the iOS device backup, click it and press the "Delete" button.
In a similar way, you can delete the data in the iTunes application from the iTunes section. Movies, TV shows and audiobooks will be displayed here.
5. Automatically using CleanMyMac X
manual cleaning method is effective (I can use the steps listed above to delete more than 30GB), but repeating it will become very time-consuming. If you are a Mac power user, you may need to do this every month.
Thankfully, certain applications can help simplify some of these steps and automate Mac maintenance. CleanMyMac X is a practical and multifunctional cleaning tool that keeps your Mac in its best condition. It can help you delete cache files, temporary files and applications. It has a smart file browser that can help you get rid of old and unused files. 
Make daily life on Mac easier
Now that you have freed up some storage space, you can start using your Mac to complete your work. Please perform the following steps occasionally so you don’t have to worry about running out of disk space.
You can make more minor changes to improve your daily Mac experience. Learn how to put the Dock on the right edge, use Stacks to organize the desktop, and start using Spaces to create a more organized desktop space.
The above is all about the "tips for freeing up Mac space", I hope it will help you!