Hey K4ik0! Osu! is probably of the better rhythm games you'll find. It seems hard at the start but as you play countless hours on the game, you'll get better without even realising you can do 4* now! In my opinion, the best way to practise is to play on difficulties where you get A's and B's most of the time. Practise getting combo first then work on accuracy. When you start getting S' and SS' and Perfect's (earning highest possible combo on map) go to slightly harder difficulties, usually increasing by around 0.3* to 0.5* at a time.
Another way of getting better is to just play without a care in the world (and watching pros like hvick225, Rafis, WubWoofWulf or Cookiezi. Many pros stream on twitch too such as Doomsday). Have fun clicking circles, fund peppy's jet
And remember, don't chase skill, let skill come to you!