I've been pondering recently what building a startup has taught me about design, as a designer. One lesson strikes me most. I used to design with two lenses: user, and designer. But building my own startup has given me two additional lenses: business, and engineering. And I feel I came out to be a more all-around product guy.
Design a product as the business owner. You are a 1-(wo)man startup. When you think this way, you will start to think deeper and you will be driven by more than design questions.
What problems am I solving? How do I know there is a need for this product? What values does my product bring to users? What hypotheses am I making and how will I validate them? I don't have unlimited resources, then how do I validate them in a lean and frugal way?
How does my product impact the business's budget and growth? What's the go-to-market strategy? How will I bring users along?
Design a product from the engineering's perspective. If you don't code, it's difficult to understand the design from the engineer's perspective.
Have I thought through edge cases? Is the design implementable? (Don't assume engineers are magicians.) Have I considered code reusability? What is the impact of my design on the performance of the application? What is the impact of my design on the release cycle?