The Classic grip for holding a watercolor brush is much like the way you hold a pen or pencil for writing. The only difference being that you (for the most part) are gripping the brush further from the business end of things. Pick up your brush and grip the thickest part of the handle above the ferrulle—the body of the brush—and hold it like you are getting ready to write a letter. Remember writing? Weigh the brush in your hand, roll it with your fingers, find the balance of the brush in your grip
Since you are holding your brush as a writing instrument go ahead and use it for that. Practice signing your name in a way that you can use to sign your paintings. It may take a bit of practice to find one that suits you so take your time. The Classic grip gives you linear control, making it ideal for flowing lines and drawing with paint. Mix up some colors, start doodling and see how the brush works as you push and pull it on your paper.
Your control for the Classic grip starts from the simple actions of the arms and wrist to the fine control of the fingers. With the control of the brush tip at hand (ha), try drawing a simple picture or two like the old masters' ink cartoons. Crosshatching, creating value with thin overlapping strokes, is best handled using the fine control this grip offers. Pointillism, the dot by dot laying in of color or texture can be easily done holding your brush this way.