Very broad question. Some steps to begin with
Decide what product or service you really want to sell.
Determine if there is a market for it
Decide what your target market is
Research what you can charge for your services
Be clear on what value you are offering customers
Determine what you "brand" is (how are you different from your competitors)
Then market, then produce good work or sell good products rinse, repeat
Of course you will have do such other things such as register a business, make a business plan, decide how much time/money you have to invest.
Simple. Sometimes, not easy. :-)