I will confess, when I chose to play Bretonnians in WFB, I let my professional world collide with my hobby. You see, I am finishing my degree in history, and to keep it short and to the point, my specialty is Medieval Europe. I also do a lot of research into geneaology, and with that comes heraldry. So, not only do I now all the symbology, I know how to research particular family crests.
My own families coat of arms:
This lends itself well to such an army, as a way to personalize my army, and to have some real pride and sense of connection to the army.
All heraldry will have 2 primary colors, with a thrid color to use in a minor capacity. My family's heraldy is relatively simple, being only 2 colors and 2 gold bars on a blue field with a gold bend(diagonal). I'll go into more detail below about how to do custom graphics for the heraldry in a bit, lets stick with the design first.
Just like painting anything, you should work from light to dark. I have a heck of a time working with white and yellow, they just seem to disagree with me. I started by priming the sheild gray, then completely pinting the shield Vomit Brown. Then I built up painting the entire shield yellow, to ensure that would be a bright and vibrant color. Next, I masked off the bars and bend. Tamiya does make some model masking tape, but I just used regular blue masking tape I picked up from Home Depot's painting section. I just cut the tape into small strips of the desired size with my hobby knife. Once that was masked off, I could paint the blue part of the shield, and it was done. Rinse, repeat 4 times on the horses coat.
Now not all coat of arms are as easy.
This is the coat of arms of the royal family of England. Queen Elizabeth & Prince Charles family. Even in miniature, this coat of arms would be possible to do.
The easiest way would be to put it thru photoshop, and print it on water slide decal paper. Testors makes 2 kinds, clear & white, and they are readily available at your local Hobby Lobby, Michael's or craft store. BE CAREFUL. You must also pick up a can on decal bond spray, to lock the image in place! Otherwise, the ink will disintegrate when you put the decal in water.
I prefer to use the clear paper, then I can overly they symbols on whatever color field without having to cut too close to the image. For something as complex as the Windsor coat of arms, I would actually go with white, and print the whole image.
I hope this makes heraldry a little less intimidating to paint, regardless of whatever army you play. If you are interested in looking into your own family heraldry, you can visit House of Names. Their search engine is pretty good, but of course individual familes crests and arms will vary depending on about a billion factors, so it is not 100%, but it's a step in the right direction.