...is probably more art than science, but we offer the following advice and tools to make it easier.
1) Give them a reason to engage by demonstrating the value TO THEM of using GoToList. You could show them the app "live", or take screen shots (easy from your phone, just hold down the on/off and main button at same time) and email them examples of what they'll see. People are much more inclined to engage when they understand there's something in it for them. And we think that's an easy sale with GoToList ...
2) Don't make it easy to ignore you by shifting your old communication processes to the new. Share your group calendar on GoToList, and stop sharing it the "old" way (typically email attachments) so they have a good reason to engage with your new communication efforts. Put useful information on InfoPage that's available to your Members anytime anywhere on their phone.
3) Check your Members' status by going to the List Management tool and its Member page, where you can see the current status of each, and with a few clicks send reminders to those yet to sign up.