There are lots of good resources as mentioned by others. Here are some starting points.
Start with a list of ideas
- These ideas should be solutions of problems either you face or you see others face
- Find 10 people you can talk to about your solution and make a list of features
- Pick the core ones and build a functional prototype that people can use and give feedback
Start with a problem (space)
- Look for problems that people complain about or ask questions (an analysis of Ask HN is a good source to start with)
Here is one story I read today (I think I found it on HN!)
https://www.linen.dev/s/linen-community/t/545988/from-idea-t...
Wish you all the best. You already took a good first step by asking a question here.