Well, i swear by CleanMyMacX - it does things native tools do not do and cleans out a lot of unnecessary logs etc which over years can take up several Gb. in fact if you've had the mac for any length of time it's highly likely to free up at least ~20 Gb of storage (not only based on my usage from from my wife's laptop and friends as well).
Especially useful is that it will delete 'purgeable space' - this is space that seems to be free but has not really been cleared by the OS. Theoretically the OS will purge this and offer it up when needed but in practice when wanting to install huge files it you'll get the response that there isn't enough free space even though the OS may report that you do have enough space. Lots of nice features like that.
As mentioned it can also graphically show you your various directories in terms of size and this lets you hone in on larger folders where there may be stuff you've forgotten about which can easily get rid of to make more space.
Another app that does this well is
DaisyDisk ('low tech' approach with no automated clearing but a nice visual map of your folders by size that lets you investigate what most of the storage is taken up by and choose to remove it yourself).
CMMX does lots of useful things and i can't recommend it highly enough if you're looking to create more free space but can't find something to delete. It also features other tools that may occasionally be helpful like managing launch agents, do a full uninstall (when you delete an app, it will search and find all related folders in the Application Support, Preferences etc and offer to delete these as well) and lots of other useful maintenance tasks for OSX.
As mentioned I use Malwarebytes Premium (my bank provides a licence for this) as well as Little Snitch (an excellent application firewall) and never has there once been a suspicion of malware of any kind. And it's highly unlikely Apple would approve this on the app store if that were the case...
If you don't trust this then have a look at DaisyDisk mentioned above - a low tech approach but also quite helpful in localising forgotten folders full of deletable stuff...