SEO, Copywriting, Email Marketing, SEM, Graphic Design or whatever you choose to focus on a certain market to position yourself as an expert.
Take advantage of your network, both online and offline.
Start connecting with other experts from your niche to get tips, hints and wisdom.
You don't need a fancy website, but you need to have presence online somewhere like Facebook, Instagram, LinkedIn, Twitter etc.
Look for companies or businesses on LinkedIn, Facebook groups, Instagram, indeed who needs services you are offering and send them e-mail to offer your help.
Facebook groups are Goldmine to get clients from any niche.
Be active there and feel free to connect with potential customers.
Fiverr, UpWork, PeoplePerHour etc., are some of the great freelancing platforms where you can learn to market yourself and get clients.