The more I’ve worked in product design with startups, the more I’ve realized there’s no real process to follow. Every challenge is different and you really never know what’s around the corner. But if I were to define my rough process for effectively shipping quality products, this would be it:
First, understand the problem, business goals, user pain points, and the target audience. This can include doing interviews internally with the team you're working with, or conducting user tests with existing customers. I'd work with a UX researcher to find the right users for a study.
Next, I explore possible solutions by brainstorming, sketching, chatting with other designers, reading about solutions others have come up with online (if applicable), then sometimes developing wireframes, but most importantly building a prototype.
After I have a working prototype it's back to user testing. I think getting things in front of users as soon as you can is super important. Rapid iteration in this stage can be really helpful, but sometimes I'll do a full test and take all the findings and propose something new after fully digesting the feedback. After talking to users, I'd show the final solution to stakeholders and present the initial ideas, my way of getting there, user feedback, and my final proposal.
Finally, using stakeholder and user feedback in combination with quantitative and qualitative data, we launch something and the process starts again from the beginning.