You can get fun and creative in how you present it as well. You don't need to just mail it out. Plan a special tea or luncheon at a nice restaurant or ask them to join you for a spa day to celebrate the occasion.
Once they've agreed and you start moving on with your planning process, keep them up to date on all of the happenings. Let them know when you need them. Use a cute card that states when the dress fittings are, when the hair appointments are scheduled and any other event is scheduled for.
These special cards can be customized to match your wedding invitations and reception stationery.
And if your friend(s) hasn't attended a wedding or been a bridesmaid before your wedding make sure they know what you are asking of them. You could even get them a bridesmaid's guide. Don't assume that every person knows exactly what a bridesmaid's role is in the wedding.
If you're a bridesmaid in an upcoming wedding here are a few guides I have found from various wedding websites:
- 10 Ways the Bridesmaid Can Help The Bride
- Ultimate Bridesmaid Guide
- 11 Tips to Giving a Terrific Toast