Should I ring my bell before going around corners?
You are from Germany so German laws are relevant. In this case §16 I StVO.

(1) Schall- und Leuchtzeichen darf nur geben
  1. wer außerhalb geschlossener Ortschaften überholt (§ 5 Abs. 5) oder
  2. wer sich oder andere gefährdet sieht.


Attempt at translating to English:

(1) Sound and light signals may only be used:
    1. when passing (overtaking) outside urban areas (§ 5 para 5) or
    1. when seeing yourself or others at risk


So if you see a danger you may use it. 

For practical terms it depends, as always, on the situation. I like ringing my bell, but I'm cautious with it. Too often I have seen that people are confused and stop or go to the wrong side or something. There are a few corners though which are quite narrow where I can't see what's coming where I make it dependent on my speed whether I ring or not. If I'm slow enough to stop in the case of something coming my way I'm often silent. When I'm faster I warn people who might hide behind a corner. Often it is better to ring once too much and annoy some people than not ringing and having an accident.

Greetings from Munich, btw. :)