Look in the ...
01. '/Library/Fonts/' and '~/Library/Fonts/' folders (leaving the '/System/Library/Fonts/' folder alone).
Create a '/Library/Fonts_disabled' folder and a '~/Library/Fonts_disabled' folder - moving any excessive (none Apple provided) fonts, you do not normally use, to the respective 'disabled' folder.
Go to 'google
', etc. and search for Mac font management tools, etc.
02. '/var/vm/' folder for an excess number of and quite large in size (100's of MB's, or in GB's) 'swapfile' files. Use 'Finder's 'Go, Go to Folder...' menu item (paste in '/var/vm/', less the single quote marks and click the 'Go' button) to open the 'vm' folder.
If you do delete (trash, and empty the trash) any 'swapfile' file(s), delete them all together.
03. '/Library/Logs/' and '~/Library/Logs/' folders (and any sub-folder), for files in the MB's or '.logx' (where 'x' is 0 to ...). Use 'Finder's 'Go, Go to Folder...' menu item to open the respective 'Logs' folder.
Trying to trash (and empty the trash of) some log files still in use will result with a 'Trash' alert box displayed, stating 'The operation cannot be completed because the item "x" is in use.', where "x" is the file still open and in use, etc.. With 'Console' ('/Applications/Utilities/' folder) one can view and clear the contents of the user accessible '/Library/Logs/' and '~/Library/Logs/' log files.
Another way to delete 'log' files is to use the 'rm' (a very destructive UNIX command) in 'Terminal' ('/Applications/Utilites/') or via the AppleScript application 'Script Editor ('/Applications/AppleScript/').
04. '/System/Library/' folder for the files 'Extensions.kextcache' (typcaily, no greater than the low 100 KB's) and 'Extensions.mkext' (typically, in the low to middle MB's). If you do delete these files (together), I suggest you restart (reboot) your Mac.
As always, be very careful (what you click on, drag about, delete, etc.) when in the '/System/' folder.