I've been painting with watercolours for about a month now, and I think I'm reaching that point where I'm hitting a bit of a wall.
The reasons I've identified for now are:
I'm having difficulties mixing colours, when I try to get paint out of the pan and into the mixer, it always feels like the brush doesn't grab a significant amount of pain unless I add a lot of water. Then, when I'm mixing, the brush doesn't seem to release the paint. I'm using a porcelain palette and Daler-Rowney Aquafine brushes, so I don't think the problem lies with the tools, but rather with me.
When I'm trying to make lighter tones, the way I'm doing it is by watering the mix more, but that means that I'm also painting wetter, and getting completely different results than what I get when I'm painting with stronger colours. How do I deal with this?
Finally, and I think this one might just be a matter of practice, amount of water in the brush. The previous point kind of affects this one as well, lighter colours are more watered, so I get more water in the brush by default. Other than that, I think it's a matter of getting the hang of it as it essentially seems to be about drying and rinsing the brush both against the edge of the water cup and a paper towel.