One might think that the essence of creativity and freedom of expression is abandoning discipline, and creating spontaneously, but in the case of watercolors, discipline is the essence of freedom. Watercolors respond instantly to pressure, to water, to the amount of time allowed to elapse between strokes. This can be intimidating to the untrained painter, but for the disciplined painter it is invigorating. Discipline does not stifle creativity here, it makes it possible.
The best way to discipline yourself with watercolors is to repeat yourself, over and over again. Instead of using new colors and subjects all the time, repeat the same ones. Not only will this exercise your perception, but you will also learn more than you would by changing your subject all the time. At first it may seem tedious to do the same exercise over and over again, but as you get into the practice of doing it, you will start to notice subtle differences that you had not noticed before. Slight differences in pressure, or in the amount of water used, or in the order of certain strokes will become apparent. The more you repeat yourself, the freer you will become. Mastering something is not a single occurrence. Mastering something is a day-in and day-out practice.
Another way to discipline yourself in watercolors is to make your decisions beforehand. Don’t make rash decisions as you are painting. Instead, decide ahead of time how you will paint. When you will introduce the pigment, when you will stop, when you will allow a certain part to dry are all decisions that you can make ahead of time, and in making them ahead of time, they will be far less arbitrary than if you made them on the spur of the moment. You will not remove chance from your painting by doing this, but you will make it a disciplined chance. Freedom of expression does not lie in arbitrariness, but in educated arbitrariness.
Finally, discipline yourself by limiting yourself. Use fewer colors, fewer tools, smaller subjects. If you place limits on yourself, you will be forced to think more deeply. You will discover that you have habits which you never knew you had. And you will find that watercolors are more expressive with fewer tools and colors. The more you can remove from your toolbox, the more of yourself you will be able to put into your painting.
Eventually, with discipline, you will be able to abandon yourself to the process of painting, and yet remain fully in control. The discipline will become so ingrained that it will become automatic, and you will no longer even need to be aware of it. There will be times when the painting will seem to paint itself, and this is when you are most free. Your mind will no longer need to make so many conscious decisions because your body will have been so disciplined that it will do them automatically. When you learn to paint watercolors through discipline, you will learn to abandon yourself to chance. Discipline and chance are not opposites. They are merely different sides of the same coin, and it is through discipline that you will learn to see this.