1: Autoconverts (maps for standard that you play with mania mode) have OD10 timing windows in mania mode, regardless of what OD setting the original map has. This makes the timing much stricter than a mania map at the same difficulty will be (OD10 is fairly rare in mania). Also, Autoconverts have awkward patterns, and rhythms that do not make any sense in a mania map. Please consider focusing on mania specific maps instead.
2: Accuracy is a skill that takes time to develop, period. Even if you're at a skill level where focusing on accuracy makes sense, it takes a lot of focused practice to improve your accuracy by a significant amount.
3: Accuracy also improves as you progress in difficulty. I don't focus on accuracy, and I can consistently 99% most maps under... 3.5 stars, or something like that (I'm not sure because I don't pay much attention to those maps anyway) without any effort at all.
4: If you decide you absolutely want to focus on accuracy, you need to focus on playing stuff that you can at LEAST S consistently. But, by focusing on those maps, you will stop improving at harder songs, and could even get worse at those songs. For example, if you focused on stuff you could S right now, you might actually lose the ability to even pass big black, if you spend too long working on accuracy.
5: Accuracy REALLY doesn't matter until you get much better at the game. an SS on a 2 star map is not impressive, ever. An A on a 4 star map will ALWAYS be more impressive (AND worth a lot more PP).
6: The biggest tip that anyone can give you regarding ANY question about improving in mania is:
PLAY MORE
It doesn't matter how long you've been playing, the ONLY way you will get better at ANY skill in mania is by playing more. I've been playing music games for ~13 years or something now, maybe 14 (I forget when I started), and trust me, if there was a way to get better without playing, I would have heard about it by now.
Why is the text sixe capped at 150? That last tip deserves to be at LEAST twice as big to really get the point across.