If you already know 4LLL after 2 years, you should learn full PLL and 2 look OLL (which is part of 4LLL) and be more efficient in F2L and the cross, when I was in sub 40, my problem was the cross and F2L, after I learned to do the cross on bottom, and be more efficient in F2L i was more than sub 40, and also be more fluid in your solves, try not to pause. Be not just fluid in Cross and F2L, also be fluid in last layer as I talked about using 3 look last layer (Full PLL, 2 Look OLL), and finally try to be faster in your transition from Cross to F2L and also F2L to Last layer, so the least in your priority is spamming TPS and learning full OLL as those are not needed until you reached sub - 20 or so.
I think this is the most generic answer for help.
If he doesn't know F2L, what's the reason to learn 4LLL? order : Beginner's method -> Transitioning from Beginner's method to CFOP by learning F2L -> 4LLL (2 Look Oll, 2 Look PLL) -> 3LLL (Full PLL, 2 Look OLL) -> Efficient cross and F2L and Cross to F2L transition -> 2LLL (Full OLL and PLL) You can do the 3LLL and Efficient F2L + Cross and cross to F2L transition steps at the same time to be faster than sub 40.
Also the last most generic answer to this question is, Practice. in the end, just that, even Feliks Zemdegs is fast with just OLL and PLL because he practices like a career and not a side hobby alot.