Start off by taking three sheets of blank paper and then writing or printing out the words, save the date on them. It would be smarter to use slightly heavy paper, as compared to normal A4 sized paper that you find in printers. The font should be big enough to be read from a far place , and block letter usage is encouraged. Now get another piece of paper and write out the date on that piece of paper.
Once you have done this, go ahead and take a picture of the two people who are going to be getting married. Now make the couple hold the four cards, so that save the date, and the actual date of the event are visible in the picture that you are going to be taking. Make sure you take a couple of shots, so that you can go ahead and use the best one. You may opt to make poses in the pictures as well.
Print out the pictures and print them out in a size that is easily shippable and one that won’t prove to be too much of a hassle to the people who you are sending it to. Once the pictures have been printed, attach them to a magnet sheet, with the adhesive side being the one where you place the pictures. This will get the pictures to stick to the magnet. Now all you have to do, is wait for everything to dry out and then ship out the magnets individually.