Studio Ghibli Fanart

I did a fan art piece a while ago for Studio Ghibli and I've been meaning to post it for a while now!

I've been testing some watercolor brushes recently and this piece was one of my victims. I used the fifth brush download set in the following site:
https://designmodo.com/30-sets-of-watercolor-free-brushes-for-photoshop/

Tip of the Day:

I use pixel locking for a lot of my artworks to help me get clean straight lines and blend colors without worrying about going over the border. I also use the Marquee tool to outline the shapes I want, for example the robot in the picture? All done with Marquee.

How do you guys get clean edges?