During a live workshop I had about two weeks ago. I wasn't able to find the brush I want to use in the middle of demo. I continue on because I didn't want to pause the demo just to find one brush. So I settled for a brush that's a bit too big for what I wanted to paint that time. Turns out it wasn't as bad as I thought it would, because it forced me to approach things with broader strokes.
This is what I usually suggest people do - Use a brush that's too big. I often see people try to render a simple shape with multiple small brush strokes using a small brush. That makes a painting looks "jaded". The difference between watercolor and other medium is the sense of freshness and liveliness. Dabbing in watercolor painting will take away those quality very fast.
If you want to paint a powerful picture that looks fresh and alive, you have to learn to paint with bigger strokes in confidence. You have to think twice, paint once. 60%-70% of my painting is done with my size 12 squirrel brush. It's not until I start get into detail such as small figures and car will I use a smaller brush. And even with a smaller brush, I try to paint as few brush stroke as I can.
Think about how many shapes do you need to paint for an object, and use as few brush strokes as you can to paint it.
I used to over work a lot. I didn't have the courage to go bold with bigger brushes. I was really afraid that I will mess it up. So I took a smaller brush and carefully paint a simple shape with many little marks. When I do that the whole painting look like a mess, because this way of working is just not suitable for watercolor. Unlike oil, watercolor dry much faster. So while you paint many little strokes with a small brush, it is likely that it will get into parts that's 1/2 dry. When a layer is half dry, any wet paint can create bad looking edge when painted on. This is why I suggest people use a bigger brush and paint one shape with one wash.
If you been painting with small brushes, try use a big brush and go broad. Nothing looks better than a big, confident stroke.