It’s mostly passive, to be honest. About 20-30 recruiters reach out daily, so I typically tell them that I’m only willing to work remote contracts (if I’m not looking for something full time) with a bill rate of $125 / hour or more. It only takes one out of a hundred to come back with an opportunity that brings in 20-25k per month for six plus months that I can do in addition to my day job to make the effort well worth it.
There’s so much work out there - let recruiters find it for you and be super selective if you already have income. After a while, repeat business will allow you to raise your bill rates. A motivated engineer willing to put in the work can pull in $300-$400k per year, even in middle America, without trying to source work for themselves.