Whether it succeeds or fails, each project you launch is a stepping stone towards your next idea. Don’t bank so much on the success of one project that you don’t move on to the next one.
Do common things uncommonly well to set yourself apart.
Don’t force every idea to become a cash cow; leave some art just for yourself. You might still make money off of it, but don’t create it for that cause. Focus on the purity of the craft and let other endeavors (artistic or not) pay the bills.
Time spent perfecting your craft is not time wasted, and neither is time spent earning a living. Find the balance and appreciate both pursuits.
Get the guidance you need on the path to becoming a better illustrator.