I wrote my PhD in development economics but I guess some of my experiences with choosing a dissertation topic could relate to you too.
First and foremost, start from a topic that you are passionate about: you will spend several years focusing on all the facets of this topic and passion is certainly something that will keep you going.
Take your time and explore really well the existing literature: do not rush the choice process and allow yourself to follow several paths and options with regards to your research question.
Be realistic and try to pick a topic (and a methodology) that can be explored within a certain timeframe; while one certainly wants to be comprehensive, it is often best to limit the scope of your research very clearly and keep it focused to avoid being unable to tie all loose ends in your thesis.
Seek advice and bounce ideas back and forth with your PhD advisor but also with colleagues who work in similar fields. Do not worry to ask for feedback even on half ripe ideas and do not fear criticism, it will help you realize whether you are following a potentially yielding research path.
If you field allows, try to explore interdisciplinary topics and identify since the beginning researcher and fellow PhD candidates whom you could collaborate with. I've done my PhD work in a highly interdisciplinary team and, while it has been hard to align interests, work streams and timelines, I got invaluable feedback (and criticism) throughout the research cycle and I got to learn a lot more than if I had worked in isolation.
I hope this helps,