One thing that should be at the top of your agenda at all times is showing your subscribers that you care about them. This is especially true in some niches where people are going through a difficult period in their lives. It doesn't really matter which niche you're in, however. People are more likely to be responsive if they know that you care about their needs and wants.
By simply empathizing with them and showing that you know exactly what they are going through, you will appear as more trustworthy.
In fact, you will be more trustworthy.
It should be easy for you to do as you are an expert in the topic and you know a lot about the people in your niche. If you're not quite sure about what they're going through, you can always visit niche forums and read posts written by people in the niche.
For instance, if your niche is pregnancy fitness, then visit pregnancy message boards and search for “exercise” to see what questions, comments, and concerns your potential readers may have.
Bottom line: Show your readers that you care about them. How? Actually care about them and then follow through.