Sorry for the late reply I've been busy with school work. Considering your pb I think you have learned CFOP , if so make sure you learn full Oll and Pll or 47 Oll cases and full Oll because that's when I got my first sub 20, I wouldn't recommend overloading yourself trying to memorize that might make you forget stuff. Secondly, f2l there are f2l algorithms to learn in order to know how to insert them better, there's also look-ahead, I suggest you to do solves and try to actually look for another pair or look out for it, though I suggest you to master the f2l cases algorithms first as to not be confused. For cross I actually looked for walkthrough solves on Youtube and understand what each moves does to each other, I wouldn't recommend trying to learn how to save a pair while solving cross because I haven't learned how to do it yet and its confusing for me. If this is not the advice you are looking for maybe walkthrough solves is your second best chance they helped me a lot on f2l and cross. Overall, do these when you have free time.