I actually did this awhile ago but had forgotten how much I love it and thought I’d share.
You can pick these patches/motifs really cheaply on ebay (or if you’re in Sheffield, there’s a really good haberdashery stall on the Tuesday and Fraday market on the Moor )
This one cost me £8 which isn’t cheap but for me was worth it as I’ve turned something I didn’t wear in to something I love!
The patches in the bottom picture i picked up for 74p from my local Oxfam.
This almost doesn’t need instructions as it is so easy but if you haven’t done anything like this before start by pinning your motif on to your garment and sew around the edges using straight stitch making sure it’s pretty secure. I haven’t tried to wash mine yet but as it’s pretty big I’ll probably stick to handwashing it from now on. Voila, you have yourself a lovely new coat!