Watercolor is what you Don't paint
To have light in the watercolor, you have to paint around it to preserve it. You leave the white of the paper for highlight. You can use white gouache to paint the highlight you lost, but it just doesn't feel the same.
There's also something what I'd like to call the "breathing room". That is, when you put down the washes on a rough paper (it has to be rough or at least cold press paper). You often get little sparkles of white within it, and they are magical. Don't fill in all the white spots. The paintings will feel dead when you try to fill everything in, because you didn't leave any breathing room.
Having breathing room makes your painting more alive, and they also create visual interest. Because they break up the flatness of an area without distracting the big picture.
The impact of your watercolor painting is what you don't paint. Once you paint an area over and it dries, there is no way to get the white of the paper back. Therefore, as you paint and put down washes, ask yourself what you should leave out.
Lastly, these sparkles happen naturally and randomly. You can influence it to a certain degree by painting faster stroke and dry mixture. But you can never and shouldn't control exactly where they appear. The key is to react and work with the watercolor, observe what's happening in your painting. That's what makes the watercolor fun, because you never know for sure what's going to happen. Remember not to try so hard to control watercolor, you work with it.
Detail of the painting Downtown Vancouver.
Notice how by leaving some breathing rooms gives more life and details.