Ok so let's turn this into a little Friday #indiegamedev business thread!
How I pick my next game project: first I pick an interesting genre, setting, feeling, vibe, mechanic that I want to explore. We all have many ideas, so pick the one that keeps occupying your brain
I then give myself 2-4 weeks time to build a prototype with that core idea up and running, so that I can figure out if it really works and if I can get enough ideas going to turn it into something more.
It's either: yes, this is something, or NO, move on to another idea
I also start showing mockups and early running code (as faulty and simple as it might be) from day 1 !
Just to see if it vibes with others. Based on how people interact with gifs, videos, images, chats of the prototype, it's a nice indication if this has merit.
For context: I do this full-time (since 2004) and run it as a business.. so that's always a key-factor in my process.
It's great to tinker with stuff, but at the end of the day, I do need to make money with things I create.
The 2-4 weeks of prototype building is purely focussed on the core-idea. This often is a gameplay feature, but can also just be a certain feeling or look. What ever it is, that's my only focus.. no clean code, no distractions, just get the main stuff up and running ASAP
And it's okay to just end the prototype after 4 weeks, that's some room you have to leave yourself. It's not a failure, circle back to the idea in a few years, right now it just doesn't work! and move on :)