The most important part of the email is the call to action and putting this in the header (if we are talking mobile) or preview pane when looking at desktop.
Frequency is very much dependant on the list, the invite and the engagement of your segments as covered in earlier questions. Again I encourage people to test increasing the frequency, this is something that often we are fearful of doing. In my experience when you do this you see opens, clicks and bookings all go up in aggregate. The more you send the more chances you have of making a booking. However you have one stat you can track which will test if you have over cooked this. Keep a firm eye on your unsubscribe rates, if you see this increase then throttle back a little, you will have tested this important metric.
There are many ways to target your ideal groups. One of the easiest is a feature we call ‘re-send’. This simply allows you to send the same message again to all those who didn’t open the initial email who haven’t opened it with a different subject line. A virtually no effort but effective method of getting your message out there to you busy recipients.
The other very obvious way is to implement automation into your campaigns. Any automation tool will allow you to set rules on sending more follow ups based on segments, and engagements, you will be able to follow up those who have not opened, those who have but not clicked, those who clicked but not booked etc. Armed with this knowledge you can tweak your content to drive results.