I would go and download @Pesi’s Watercolor brush set, and then in Krita I’ll select a brush hit F5 and study its settings. Find out what happens if I alter parameter X or Y or Z And I would repeat that for any brush I want to understand. Okay, you can also use other watercolor brushes than those from @Pesi, but him’s are those I like most. This is the way you learn brush tuning and brush making, see how other brush maker have done it before.
Additionally, you should watch @RamonM’s video’s about making brushes, you’ll find them on Krita’s YouTube-Channel.
Michelist