Image from the Empty Easel site
A few months back, I purchased a few brush pens but I haven't experimented with them yet. Today I came across this Empty Easel post on Brush Illustration & Calligraphy: An Introductory Lesson for Beginners written by Phawnda Moore.
She offers some very helpful tips such as:
"Start with some simple freehand drawings. This is a case of getting to know your brush! Play with it; see what it will do. Begin with a few simple lines: try light pressure at first, then slowly increase the weight of your hand holding the brush to make thicker, more substantial lines." (See example above)
"Move on to some curved strokes, as well as horizontal strokes. Then, when you feel comfortable, experiment with a few simple shapes—like an apple, or a leaf. As you vary your pressure, you’ll notice them start to come to life!"
Check out the complete article and then break out your brush pen.