First, do not ever go to Mike Lin’s workshops. Terrible. You would be better served pencil sketching daily. Look at shadows and light and line weight – that is all there is. Mike Lin is a gimmick. Do not spend your money. If you have trouble designing-practice over and over. It is a muscle. You will succeed, you will fail. The ratio will fall in your favor over time. I think hand graphics are the most important talent to have and you are wise to want to develop your skills. People respond to a hand drawn sketch. Computer graphics are useful as well, but do not speak to the soul. Keep practicing and do not stop. Best of luck.
