It is not very wise to follow a post featuring Busch drawings with samples of your own work. But here it is, since I had nothing else prepared.
When Disney announced the production of The Lion King way back, the animators were encouraged to start sketching at zoos and wildlife parks. These drawings are from a sketchbook dating back to that time.
I had then just found out about brush pens and was eager to try them out. The fluid lines coming out of the pen's tip almost eliminate any stiff drawing on the page, on the other hand bad drawings are still possible. You can still come up with wrong proportions or weak poses. The brush pen is only a drawing tool, but a very cool one. The thick and thin contours seem to add a little life, and by smudging the ink on paper you can achieve some rough rendering, which sometimes helps to define volumes.
Just a technique, the main thing of course should be focused observation and the attempt to put down specific poses that define the animal.