I begin with simple worldbuilding. Where are my characters? What world do they interact with?
The world and it’s rules are the rules that I follow.
I start with writing randomly, trying to find something to latch onto for the start of the story.
If I find something I like, I begin brainstorming.
A lot of ideas go through my head, which I either add or discard. And based on those, I develop more ideas and the story.
It's okay if you have writer's block. One way I deal with it is thinking of new ideas to add, which makes your imagination run wild.
I enjoy writing my stories in the first person, as you feel a better sense of immersion.