Learn by doing
There are a lot of things that you cannot learn unless you try. Doing business online is one of them.
From my experience:
Do a good deal of research before starting. Put in practice what you start learning. Real world experience is your most valuable asset.
Start with a budget. It'll be sad if at the end of the year you can't cover your domain name fees.
Don't expect to receive a lot of money from the beginning.
Reinvest some of your profits.
Plan for the future.