Using a flat brush dampen the background area with clean water.
Do one area at a time, so the forward painting edge stays damp to prevent a hard edge.
It seems to work the best if I don't pre-wet right up to the edge of the bird or flower.
Do right next to the bird and flower when you are painting on the color.
If you pre-wet right up next to them, it makes the color pool up against their dry edge.
I made some marks behind the bird to simulate flight movement.