Personal project?
1. Market research. If it's something worth doing, someone else has done a similar solution. Ideally, the competitor is a hacky solution, built off some forum, community, or an Excel sheet, and has become really tedious. If there is no competitor, there is no market.
2. Pull feature lists out of their feedback of that tool. A couple of hours reading reviews and Reddit discussions does a better job than focus groups.
3. Hack a disposable prototype. Key word disposable. It will be buggy and ugly but do a better job than the existing tool. The key is to gather information.
4. Get feedback from the prototype. Ideally do this in person - you want to see the point where people get excited.
5. Focus on the features people love. Think about suggestions and complaints. Don't implement immediately, but find out why they ask for it.
6. Iterate and improve.