Simply drag and drop the message from Mail to the Reminders application icon in the Dock. The Reminders app will present a new item in your default list with the name of the email as the title, and a link to the message. Clicking the link will open the email in Mail. You can easily set a reminder for a location or date, along with a priority from here.

You can also drag and drop an email from the Mail app into the Calendar app on a specific date. This will create a new event on that date.