the way that i started to progress, was when i defined what my ranges should be in spots and why. What should you float with, call, raise, etc. Once you start to know what YOU should be doing, you can assume other people have the same ranges to start.
Once you see a showdown, then you might be able to gather a read. But you have to start with finding out hte right play.
So, what range should YOU be flatting 3bets with? what %, what specific combos? What hands do you float with, why?
I could never move forward until I started to figure these things out for myself ( a few months back). You have to build and memorize a frame work for what SHOULD be done in common spots.
I have a default 3bet calling range memorized, its kinda tight. It's what i assume everyone has until i see a showdown that shows a hand outside that range. Or if i get a 150 hands on someone and their calling % is way out of wack with my range, i can adjust my range.
IMO, it all starts with defaults. default ranges, default plays. play a default game ( theoretically balanced enough for your limit) then adjust as you get evidence.
The place to start all this is, vs 3bets, what ranges should you fold, call, and raise, why? vs a 10% 3b, 20% 3bet, 30% 3bet. what is the math for everything? how often can you bluff 4bet? you need to figure it all out for yourself.