I think what you include in each email will be personal to you, but essentially, it's best to genuinely help people. So if your audience have a lot of common questions, or pain points, or struggles, than anything that will help them and give them a micro win is helpful to them.
Another way to look at it is to imagine you are sat in front of one person from your audience (in a bar, or coffee shop). You are having a chat, helping them with what ever issues they are having. That chat could be a series of emails. I like to think about it in those terms - human to human.