Study, Understand, Learn !!! Whether it be natural materials or artificial materials.
The best fly tyers will study all materials (even keeping up on the latest materials, find new uses for older natural materials, or find new materials themselves (like a craft store); keeping up to date is important to stay on the cutting edge.
How do these materials react in the water (ie. movement, color, refraction) and how best does it add to imitating what you want to imitate ??? Come to understand through constant experimentation at the vise and on the water how the material you use results in fish strikes (the trigger psycology). Learn how best you can use this material, in what patterns, and even your own designs. The materials you use, and how you use them can make the difference between a go-to pattern or one that will collect dust in a fly box !!!!