Generally I got into the 5000s after playing for three months, a lot of ups and downs; here's what I can share,
1) Beatmap offsets,
There are maps with faster bpm and slower bpm, you can always adjust the beatmap offset according to your preference.
Whenever you are playing a beatmap, there's always a hotkey that will allow you to adjust the beatmap offset before the song starts, usually its F2 or F3 for increase or decrease speed. You can look up that in the settings- hot keys area.
2) If four - five star maps often destroy you, why not go with two - three star maps?
Seriously, although challenging is a good thing, but why not get some useful pp when you have the ability to? I see people in multiplayer mode often select maps not matching their playstyle, score, ranking, etc. It's really your choice to pick up hard maps, but it is also wise to select maps within your ability range. I started to play two star mania maps, and some converted maps from 3 to 5 stars, after I picked up to four - five star mania maps. It really does take time, and you will realize your improvements. xD
3) Watch replays!
Replays of professional plays are essential to your improvement in a map, you can watch it before you play a beatmap or after. (Doesn't matter ) The point is to get use to professional speed and play style of the beatmap. It is good to follow and ask for tips from high ranks, I believe most of them have good information to share!
I don't usually use that much mods, but sometimes for fun I use fade in/hidden/sudden death for beatmaps I am familiar with. It was a mistake that I use the standard Osu! Mods, but its similar, the difference is the special part.
5) Warm-up maps
There are no specific warm up maps, but I recommend that you can find some maps to utilize it into warm up maps, the purpose of it is to get your fingers into battle mode! Don't pick hard warm up maps, pick some beatmaps at your level, and here's some recommendations:
6) Spectate! Spectate!
This is an option, but you can spectate pro players and imagine yourself going at full speed
7) Have Fun! Osu! Mania is Love, Osu! Mania is Lyfe!