My progress was like
Old method = LBL + keyhole2L
End of March - started learning Fridrich
1 week after - completely memorized 2-Look OLL and 2-Look PLL, first timed solve = sub 1:30
1 week after - jumped from sub 1:30 to sub-48
(finally optimized intuitive F2L to 3-8 moves except for weird cases, and mastered <8 move sub-3 cross)
1 week after - jumped from sub-48 to sub-40
(after practicing conscious look-ahead in F2L, grabbed some algs for weird cases)
1 week after - jumped from sub-40 to unstable sub-30
(better F2L look-ahead, faster F2L execution..finally stopped watching the cubies)
1 week after - jumped from unstable sub-30 to unstable sub-25 (consistent sub-30)
(finally moved to 1-look PLL, practiced F2L with metronome, started grinding some F2L algs)
And then, getting past unstable sub-25 to unstable sub-20 (consistent sub-25) as the biggest hurdle IMO.
The reason I think I'm constantly improving is because I don't do "blind practicing", where I just grind solves one after the other, but instead constantly try to find something to improve and work on that (except for learning all OLLs, I'll do that later

). I have a friend who started the same time as me and is still sub-60, because all he does is solve all day, which I think grinds his bad habits (such as his sloppy 15-20 move F2L) even more into his system.
And I'm currently stuck, because I can't figure out how to improve further without memorizing the OLLs (which I think is unnecessary yet, until I hit stable sub-20).