Include
Name, title, company, one phone number, website, two to five link icons, a photo or a logo. A call-to-action button if you have one thing you want people to do.
Leave out
Quotes, more than one phone number, every social network you have an account on, your full postal address unless it matters, “Sent from my iPhone”.
Size
Keep the card under 600 pixels wide so it fits a phone and a reading pane. Outromail's medium card is 560.
Images
Hosted, not embedded. Logos as PNG with transparency, photos cropped around the face, everything at double resolution.
Legal
Put disclaimers in small, muted type under the card. They are required in some industries; they do not need to be loud.
Deliverability
No tracking pixels, few links, no link shorteners from public services, hosted images on a domain with a good reputation. See our deliverability page.