Two approaches:
1) Work for one large client and essentially become an employee (consider this. a lot of startups pay good money for remote employees)
2) Work for multiple clients
Focusing on #2 here
Core rule: You want to be paid premium for quality and service.
Avoid marketplaces - it's very hard to compete on quality here.
Niche - the more focused you are on a (profitable) niche the better you can charge premium for domain competence
As thibaut_barrere mentioned - Build a brand - i would even go further - create an agency like brand. At the point is stopped saying "I" but said "we" i was able to charge more.
Dont charge by the hour but by the value - most developers charge their time - you want to charge the value you provide to the client. Read up on "willingness to pay"
Most important: Deliver as promised and always try to over-deliver in service, quality, etc. Eg try to understand why the client asks for features and not only what features she/he asks for - you might be able to come up with better solutions or anticipate future requests. Any successful project should usually lead to improved reputation and more projects and clients.
Good luck!