To keep doing it and practicing it is really the only way this faculty of our mind / spirit unfolds. In my free ebook I wrote a chapter about how to develop your clairaudience and clairvoyance. My method is being used as for the curriculum in the Order to which I belong.
Here’s the chapter.
Remember be patient with yourself too.
If you’re willing to put in the effort two or three days a week for 20-40 minutes then you will probably get results in 3-4 months. Maybe sooner. This actually works.