Find clients first and listen to what they're really trying to accomplish. If a solo founder builds something they assume people want on their own, it maybe wasted effort. Always reduce risk by selling a promise of bit more than you currently have that you can deliver on. Being a solo founder is especially risky because there's no other person to bounce ideas off of and to keep each other ground in reality.
The hard way of selling: I didn't realize it, but there was value in unsolicited selling things people didn't necessarily want like Boy Scouts selling magazines or candy bars door-to-door. It's building comfort of rejection that's important.