The designer-- my cofounder-- is someone I've known for over a year, who had an interest in being a designer but wasn't "really" a designer at that point. We sought an external person who was a "real designer" to do the icon, but they didn't really seem interested in the project and so we cut our losses and paid them.

I've been a user experience person going way back to the 1980s, so I've got quite a bit of an opinion on these things and we hashed out all the usability type stuff between us. The designer had a huge impact on the look, and produced all the image assets.

We went with a skeuomorphic design. One of the things we want to try (when we get some time) is redesigning the app with a more modern look and seeing what the impact is.

I've worked for a lot of startups in my career and one of the top two things that kills a startup is conflict between the founders[1]. I was fortunate to have someone I knew a long time as a co-founder, and previously I'd attempted to do a startup as a solo founder.

I think if you're a solo engineer, finding a co-founder with design skills and building business skills in yourself (and/or in them) is the way to go.

But best to know them for a couple years, so you might look for people you've known for awhile, if you can.

[1] the other is bad advice being forced onto them by the investors.