The easiest way to avoid having to make corrections to a watercolor is to not make mistakes. Very funny - but easier said than done, right?. We all make mistakes. It's a given.
There is a myth about watercolor that it is a very unforgiving medium, and to some extent that's true. But, the truth is, you CAN make corrections.
It all starts with using a high quality paper. Typically a heavy 300 pound paper allows for adjustments. You can "lift" paint from the paper surface, and there are undoubtedly other ways to make corrections, as well.
The way I have lifted paint is to rinse out a brush with clear water and lightly scrub over a painted area. Then squeeze out the water in the brush using a cloth and go over the surface again. The paint will be drawn up into the dried bristles. After repeated efforts, a lot (if not all) of the paint can be taken up this way. The sooner you do this after application, the more effective the technique.
These two photos show a before and after work effort. I painted this scene in a recent class that I gave. I usually have about a 45 minute window in the class to demonstrate, then turn the it over to students who try to use similar techniques on the same scene or one of their choosing. Obviously, in that short time, I am going to make mistakes. In this case, I did not like several things that happened, so later, at home, I made some adjustments to salvage the work. I removed some of the foliage on the one tree, but more importantly, I did not like the foreground. I did not like it enough, in fact, that I cropped it out of the photo. It was too cluttered, and I did not have enough green in front to match all the grasses shown in the photo we worked from. I was able to satisfactorily make these changes.
Try this on your own work. Do it carefully at first. It can save a painting that just needs a little nudge toward greatness.