As Dave said, use a safety pin; it's usually a lot smaller than the brooch pin, and it's a lot easier to get a neat pleat and the brooch squared away (with mine it matters) and then pin it down. I put one in the shoulder too, under the epaulette just distal to the button, to keep it from bunching up outboard; I guess my shoulders stoop a bit.

I wear mine higher; even with the top of my shoulder, like you would with a full plaid. In the pic you can see why.