First come emotions.
When it comes to design, I like to think a lot in term of emotions. My starting point is to figure out the kind of emotions/sensations I want to evoke in people in order to better support the message conveyed through interaction. This usually leads to a very small concept document and to some interactions schemes made on paper. I like to quickly try to visualise what I have in mind.
Then wireframes and interactions
Once I have a rough idea of how my interactive experience will look, I start defining it through wireframes and interaction prototypes. I do that in Framer, Marvel or Unity, depending on the complexity of the interaction and the scope of the experience. With this step I try to capture the core essence of what I want to do, so to have a minimum viable product as soon as I can.
At this point I usually start thinking about the microinteractions that can help me to make the application more "physical" and relatable. The animations are still rough here, but I try to set a direction to aim for.
Analysis and first assessment
Now it's time to analyse what it has been done, possible doing some first tests. I like to make a list of observations, where I put everything that works or that doesn't. Then I write down all the results I have obtained through this first iteration, the hypotheses of what can be added and how and the possible corrections that have to be made to improve the design. Everything that doesn't work and cannot be corrected is put away. The aim is to have a core of features that really work.
This way I have a first draft document of what I want to do and how. I like to think about it as a map that I constantly update while exploring an uncharted territory.
When the first prototype is convincing, I start production. I usually start by refactoring code from the prototype (if applicable) and I detail everything better. I put in the final assets, decide the definitive flow and so on. I like to keep this process iterative as well. For that reason I set up goals and deadlines and update the observation document accordingly. This way the project naturally grows towards the final product. The idea is to keep the goals central and then to change and detail the mechanics and interactions while iterating, keeping the process flexible and adaptable to change.
Design and production are thought as exploration. I know what I want to reach, but the way I will reach it is to be defined. This is central in order to deliver a great product.
Solo vs. Team
My design process works equally well when I'm doing solo production and when I work with a team. I like to involve everyone in the design process, for I don't really believe in the idea man. I think good ideas can come from everyone. In that sense, both the prototype and the observation document are extremely collaborative and everyone is encouraged to share their insights. This has the side effect to make everyone feel equally involved in the process and important, it motivates the team and it improves the quality of the final product.