i try not to really use references when drawing filigree. it's a weird mental training i do- but if i am designing something for a client of mine or whatnot i like to go to etsy (.com) and look at filigree jewelry or shutterstock (.com) and search for baroque, filigree, floral designs and take ideas from that and reuse them elsewhere.
it's mostly trial and error for me though. i force my brain to create something with flow and an organic feel.
before laying down the leafy like density i draw a bunch of loose swirls and have them tumble or twirl around in my desired shape and then i slowly sketch in filler an then eventually refine my drawing.
i hope i helped a little