Start off by looking at interaction, are they clicking the link? Are they opening the email? Next, you need to look at engagement, is the customer providing you with information? Are they signing up to your services? Next up is good ol’ participation, have they formed a deep connection with your brand? Do they boast about purchases? Tough Mudder is a great example of a brand that has developed great engagement with their customers by reflecting the personalities and goals of the target audience.