Be Mindful of People's Time

It’s a great set of points that also apply to meeting someone at a networking event, a cold call, or your first meeting with a prospect.

Three Additional Suggestions For an Opening Email

These apply to a situation where you have not actually met or spoken with the person before.

Mention a friend in common: if you have a friend in common or someone suggested that you e-mail or call, mention that in the firs two or three sentences. And be mindful that you are now potentially spending that person’s social capital with the person you are talking to as well as your own.
Mention an article, blog, podcast, or video: if you liked a particular article, blog post, podcast or video they did then mention that with a link and add one sentence about what you learned from it or why you liked it.
If you heard them speak: if you have attended a talk they gave mention the specific date, location, sponsoring organization or event, and topic. Add one or two sentences on key insights you took away.

Outline specifically where you met or spoke: date, time, event, location, any other detail that would make it particular or memorable. You want to show that you have actually met them and this is not a cold or opening email.
Document actions you have already taken: if they suggested that you do something or investigate something when you last spoke, outline what you have done to follow up.
Outline other research you have done: if you have done additional research on them mention an article, podcast or video that you reviewed and what you have learned from it.