@steele In the search box, put those interests of yours in with a hashtag in front of them. In the search results, pick "hashtag". Then select the hashtag of interest, and in the middle column near the top is a person with a plus sign on it. Click that, and you've subscribed to all posts with that hashtag!
Also, had you made that post with hashtags in that list, you'd have attracted people following those hashtags.
This lets you follow a certain kind of interest.