For two weeks, keep a log of all the things that seem to be missing and all the problems you encounter in life.
Use a platform that allows you to easily add to the log on your phone. You want to be able to pull out your phone and jot something down quickly whenever you notice something missing or problematic.
This reading is helpful for context: www.paulgraham.com/startupideas.html.
As PG suggests, turn off all of your other filters, including whether the thing that’s missing could be a startup idea. Also don’t worry about whether the problems you encounter are too trivial. The idea is to get this background process running, and get you in the habit of noticing more potential startup ideas.
By the end of the 2 weeks, there should be plenty of items in your log.