Just like with a musical instrument there are multiple ways to practice and get “seasoned” in what you do. With drums they recommend to play on a regular practice pad to warm up and to get quicker/stronger, than to go to the full drum kit. Alternating this as a regular discipline will get you to your goal of mastering that certain activity faster with more consistancy. This is no different with the Graphic Design world, I have learned that in order to be as effective as you can you have to regulary practice different types of mediums in art. This might consist of painting on an actual canvas with oil based/ acrylic paints, and after doing the same things in Photoshop/Corel or drawing with pencil and paper and transfering those same techniques with a Wacom tablet in said programs.
I try to always start out with sketches of the designs I’m trying to pull out of my head, not only is the process fast and allows you to leak your imagination but it also gives the visual stimulus to add or erase right on the spot. You dont need to worry about being to messy or precise with your strokes, just let your mind flow to the paper and then you can put that into your program of choice for refinement.
Here are examples of very quick sketches: