Beginning artists usually buy a wide array of brushes; one of each from a catalog or store. After their skills are more developed, artists frequently pare their selection down to three or four brushes that they use over and over for many different techniques.
Filbert brushes make great leaves or round shapes for pollen and highlights. Liner brushes make great branches on trees or masts on sail boats. Experimenting with what each brush can do is a great way to hone your skills. When push comes to shove, most artists end up using only a few favorite brushes for every painting.
There are other techniques that can add depth and character to your artwork. An artist friend used a tiny squeeze bottle filled with paint to make intricate scroll work on a painting. He has created some interesting backgrounds using lace doilies or trellises and spray painting over them. Other see-through materials and shapes can create interesting patterns that add depth.
Be creative! Experiment with each technique and each brush until you find your own unique rhythm--your own favorite brushes.