There are many ways to go about this but the best method is to simply sit down and interview customers who've bought from you in the past.

It may be necessary to give them an incentive but don't lead with that. Initially, just ask to have a conversation because you want to improve the service you're providing. If you don't get enough takers there then you can add an incentive.

When interviewing your customers isn't an options, then turn to surveys. Specifically, likert scale surveys (more here: https://www.kyleads.com/blog/likert-scale/). Likert scale surveys allow you to gauge sentiment.

For example, you could ask how often do you go to the gym:
- very often
- often
- Neither often nor seldom
- seldom
- very seldom

Using that information, you can quantify the habits of your audience as a whole. Also use open-ended questions in conjunction with your Likert scale questions so respoondents can go deeper into their feelings about specific topics. Taken together, you'll get a good idea of their habits, likes, and dislikes.

If your current customer base doesn't provide enough responses (at least 100), then you may want to use ads or personal outreach on a platform like LinkedIn to get those insights.