That's not really something that can be answered as a "one-size fits all" answer, unfortunately.
The best way to think about email communication (or really any marketing) is that it's solving a customer need. So if you have a long customer purchase cycle (let's say real estate) then you might be answering specific customer questions in a nurture, in order. Something like:
* How to get pre-approval for a loan
* How to find the perfect house
* How to put your offer in
* How settlement works once you're successful
Each of those emails, when timed correctly, will be answering a customer question preemptively and helping to solve for that need. They could be emails in a nurture program.
You can take this example to any industry you want, and any give segmentation. If you have different products for men vs women, then maybe each of these are different streams in an engagement program, since the communications might be different.
Generally speaking, by segmenting your audience by what their needs are and what they are trying to accomplish, there are natural communications that flow from that process. And these are often what comprise your nurture program comms.
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