I'm genuinely always surprised by my lineart improvement. I still suck at designing clothes.. but the faces? the bodies? I'm really happy with that. Like, here's a link to the last reference Cameron had, that I made last year.
https://toyhou.se/7766649.cameron#98694216
The biggest aid I think that'd helped me has been making my canvases bigger and sketching with that big space. Gives so much more room, albeit it also takes a long while too. The sketch alone took me over an hour.