If you have not heard about the Family History Federations free 'Really Useful Bulletin' then take a look at the latest edition.
This edition has a fantastic article on Postcards by Helen Baggott. Helen tells of her motivation to research the family that sent/received the postcard and their background. It brings a new source from which if we are lucky to find a card from our family can add details that may not be available elsewhere.
You can subscribe to the Federation's free Bulletins by going to the federations web site and subscribing through the icon at the centre of the main banner.
Yes, the FHF know it says 'Newsletter' rather than 'Really Useful Bulletin' but it does not detract from the articles that are published in each edition.