A great overview of getting started with saving your own seeds.
http://mikesbackyardnursery.com/2013/06/saving-seeds-abeginners-guide/
Also check out the WSID article on How to Harvest and Save Tomato Seeds. And for folks looking to get more advanced resources, check out: Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners, 2nd Edition
This is a companion discussion topic for the original entry at https://peakprosperity.com/saving-seeds/