I made these beauties (and more!) for my sister. These bookmarks are the same as this one here, but with a thin wire on the branch and using a smaller hook. (Pattern: http://www.ravelry.com/patterns/library/little-owl-bookmark)
So here's how I worked with the wire:
1. Curl the end of the wire, but don't close it yet. Leave a gap so you can insert it in one of the stitches.
2. Work on your base chain (45 ch). Insert the wire on the second chain from the hook - the chain where you'll do the first single crochet (in the pattern it says dc - UK terms - but I'll be referring to the stitches in US terms). Don't close the loop yet.
3. Line the wire along the length of the base chain. The wire should be on top of the yarn. Do a couple of single crochets, working over the wire and the chain. When it's long enough (about 4 or 5 sc), close the loop on the wire, making sure that it's still hooked on the chain.
Aside from adding a wire, I also worked the leaf on the branch, instead of stitching the leaves on the branch.
Make the first half of the leaf as instructed: ch 6, ss on 2nd ch from hook, sc, htr, dc. On the last stitch, you're supposed to make 4 dc's. Do the first dc. On the second and third dc, before doing the last yarn over, insert the hook (which has 2 loops) on the stitch where you want to place the leaf. Yarn over and pull through all the loops. Continue working on the second half of the leaf.
Don't get frustrated if the wire cuts through the yarn or if it's taking more time to work on a piece. I had several do-overs because of this. Just be patient and you'll soon get the hang of it.