L.B.
I have spent over 15 years in non-profit in some capacity or another, from grants administrator to Director of Operations.
Really, any sound job experience can make the transition. The only difference between for profit and non-profit is the bottom line - non-profit puts their "earnings" back into their programming instead of in their pockets.
If you have strong admin skills look for an administrative capacity position with a non-profit. They need office managers and admin support persons. Sales experience can translate into donor relations or fundraising - let's face it, fundraising is sales. LOL
Volunteering is a good way to build a network in the non-profit community and a good way to learn about the different organizations in your area. Also, look into part time program or advocate positions with your local non-profits - intern positions can also help you make the transition. If you have a specific skill set you could offer contract work to the organizations while building your experience, network and resume.
I have found the non-profit world to be very rewarding on both a professional and a personal level.