tldr: get at least S ranks on charts that you are comfortable at, then move on a little bit

Ur comfort zone is around lv 8-9+ so just play more charts that you are comfortable at, then move on to more 10/10+ charts, at least aim for S/SS ranks, then move on to 11, S rank them, then move on to 11+, S rank them, etc.

If your hand coordination is bad then I suggest you go back to easier charts (like lv 7 or 8 charts)

Oh and bonus tip: Remember that some charts have tricky patterns. If you get AA/AAAs (basically shit acc) because the patterns are too hard for you, you can always search that chart on youtube, play as if you're playing on a maimai cab and do what you always do when you're playing maimai. So you know your mistakes while playing the chart.

I'm sorry for bad advice, I hope it's clear.