I am fed up with all these useless "Delete old pictures" "Delete your trash" BuzzFeed-tier articles so I am hoping for some qualified ideas here.
What I've done so far (and how much it deleted) is:
Monolingual (2.5gb) : deletes unused languages in applications. I only kept Chinese and English. It can also delete classes for older architectures but that was only a few mb, languages is the main focus of that app. Many people say it destroys your applications but I've been using it for 5 months straight now and never experienced any problems
OmniDiskSweeper (countless gb) : like TreeSizeFree on Windows it lists directories by size. This way I for example found about 8gb of iTunes cache files that haven't been deleted, some xCode caches and simply big folders of other applications. If you "lower your standards" every session you will eventually end up even looking for folders smaller than 100mb but it's totally worth it as e.g. 6 of them already make half a gigabyte
CCleaner (5gb) : well-known on Windows but not too popular among mac users it took care of my cache files (basically Chrome (2.2gb) and Ableton(1.5gb) but it also deleted some system caches
OnyX (300mb) : it's rather fixing stuff than deleting but it also looks for some temporary files that were meant to be - but never have been - deleted
deleting Garage Band (maybe 3gb) : as I am using nothing but Ableton for music production I deleted the app and most of its contents except for some fine drum samples
What else can i do? Having a 120gb MBA I have no choice but to locate every single file that's not completely necessary. It's just weird that, without installing applications, I see my drive getting more and more filled up with junk (I guess). Of course a system won't just magically lose "weight", but I can remember being at 45gb of free storage 10 months ago and my computer usage hasn't really changed since. (I am at 18gb now)
I might try CleanMyMac 3 at some point but I haven't heard about it too much yet.
EDIT: I will include your ideas in OP if it helped, but the best hint still gets a tick tho