Well, first off, kudos to you for wanting better skills! And they pay off handsomely, because this sport is like skiing - the better you get at it, the more fun it is.
If you are working on your own, there are a number of things you can do. One is to work on hovering. The goal is to be able to sit still in the water, without moving hands or feet, for as long as you want to. This may require
moving some weight around to get balanced and also
adjusting body posture to get better trim. But being able to sit still and look at things was a big leap forward in diving skill for me.
Another is to work on your buoyancy control while task loaded. Try hovering and flooding and clearing your mask, or taking it off, or practicing an air-share with your buddy while hovering off the bottom. (Warning: Do these things initially in shallow water, because you may be surprised at how badly your buoyancy will be affected, when you begin to practice.)
Finally, you could consider taking a class that works on these things, and introduces other ideas like non-silting propulsion techniques. You don't say where in Germany you are, but German has a GUE instructor who can teach the Fundamentals class, which is where I learned these things. Various agencies also offer an "intro to tech" class, which is a bit of a misnomer, as one is permitted in at least some to do the class in a single tank setup, just to learn the skills.
Have fun with it -- practice dives can be a great way to get wet, when you don't have access to more exciting sites because of weather or logistics.
