As chrisked mentioned - definitely my previous clients and friends.

The best long-term contracts I received was through a former colleague, classmate or a friend. Recently, linkedin provided a steady source of leads (not talking about recruiters) via niche groups, 2nd/3rd connections etc.

One great site is https://whoishiring.io - an amazing job aggregator that parses (in my opinion) the best sites for work. This eliminates my need to go hunt for jobs on job boards.

Avoid freelance marketplaces like upwork, freelancer and others.