What's your workflow to create new features?

Hi!

Since yesterday, I’m trying to “design” the flow and database tables for a new feature in my app. Whenever I have to build a new feature that seems to need a lot of conditions and variables, it’s becoming quickly a mess in my head and I procrastinate and waste a lot of time .

How do you approach this? What is your workflow for designing and creating new, complex features for your web app?