So all artists have been there. You started a painting, you weren't really happy with it, so you put it away, hide it for a while... hoping that maybe the next time you pull it out it will have magically fixed itself.
Often what I will do is put the bad painting in a drawer (I labeled "Re-dos") and wait. Sometimes years pass before I come back to the painting. When the moment strikes me, it's often when I'm in a painting dry-spell. I am looking around the studio saying to myself "I want to paint something, but I don't have much time or energy... Where is something I can just play around with?" That's when I reach for the drawer. I'll pull out a couple from the re-dos drawer and get going.
Redeeming a bad painting
One of the easiest ways to fix a bad watercolor is to paint gouache or acrylic over it. Something opaque to cover up the transparent watercolor below. What I enjoy is switching subject matter. This painting of the marsh was once a painting of a tree outside of Trolley Stop hot dogs. You can't see the hot dog sign anymore, but some of the green from the tree is still visible in the clouds. Switching subject matter allows me to completely reimagine the piece, play with it, and see what comes of it.
Here is an example of some paintings that weren't terrible to start with, but they just needed some amping up. They were lifeless, dull, uninspiring. They weren't painted at the same time originally. One night I decided to paint gouache on top of the watercolor. It was a quick addition that really packed a lot of punch. They became a set and sold quickly thereafter.
Here's another example.
Some paintings are greatly improved by simply cutting them or cropping them differently. Here is an example of a time that I cut a large watercolor in half and ended up selling the right-hand side and scrapping the left.
Happy painting! Remember that all artists have to paint like 100 bad paintings for every good one we produce. Just be creative with those 99 leftover ones and do something fun with them!