Tips for levelling up my solder game?

I've been making modules and guitar effects for at least a year now. By which I mean buying predesigned PCB's, making parts orders, and soldering them all together. In that time I've upgraded to a nice T-12 soldering station, but have always just used the same 60/40 flux-core .8mm solder, no liquid flux or anything. I rarely clean my PCB's during or after construction, which of course shows in that gross white flux residue all over my finished builds. I'm not even sure how that affects their reliability or anything like that.

So, how can I level up? A few specific questions:

* How do you like to clean your PCB's if at all? Would having a tupperware full of IPA that I can bathe/scrub a PCB in do the trick? Are there any components that shouldn't be submerged like that, e.g. ICs, electrolytic caps, potentiometers? And what benefit does this have for the finished product? * Should I change up my solder? Seems like it's recommended to use liquid flux, especially for SMD soldering, but would that come with a new kind of solder or technique?

Any general advice is welcome honestly.