The process isn't complicated - just time consuming. It only requires small amounts of the materials, and no special expensive tools.
The leather you use for this can be from an old leather belt, boot, jacket, or whatever from the thrift store. Well, maybe not a boot... I'm not sure if you'd want something that's going on your head to smell like some unknown person's foot. My leather was some small scrap pieces I got from our local leather shop... they were practically giving them away a couple years ago because they were getting ready to move locations and didn't have room for all their scrap leather. The pieces were small, but plenty to make a headband. I used some medium brown leather, smooth on one side, for the branches. The flowers were cut from some thick tan suede. The leaves (well, some of them) were from a dyed piece of thin kid leather that the guy at the leather shop threw in for free because it was leftover from one of his projects. I'm assuming the kid leather is from a young goat, not human kids. ;)
upholstery thread or some other strong thread
unfinished wooden beads
glass seed beads
rubber cement (helpful but not necessary)
fabric glue if you want to attach the leaves the way I did (you can sew them instead if you don't have fabric glue)
iridescent cellophane, organza, and light duty iron-on adhesive (if you want to make some iridescent leaves)
scissors strong enough to cut your leather into shapes
needle strong enough to penetrate (heh... penetrate) your leather
thimble, plastic table, or some other hard surface to help you push the needle through the leather
sharp thumbtack if the leather is really thick like the stuff I used on the flowers
optional - an iron and some parchment paper if you're making iridescent leaves
Start cutting some thin branchlike strips from your scrap leather. I lined mine up on the plastic table we have in our living room. You can see from the lego plane that I had to share my workspace. I used some rubber cement to attach the branches temporarily so I wouldn't forget which piece went where when I was sewing it.
I then stitched a running stitch along the branches, attaching them to each other and strengthening the headband. It seems simple (and it is), but this part took FOREVER. I tried poking holes through the branches ahead of time with a tack, but it didn't save much time and then I lost some of the holes before I could get to them. I don't have a sharp leatherworking awl. After the leather branching part was as long as I wanted, I took a thin hair elastic from a package of them I hadn't used and sewed the tips of the end branches around it. This keeps the headband stretchy so it'll fit snugly on the head but still be easy to put on and take off.
When the headband part was complete, I worked on the flowers. I cut some uneven shapes in two sizes so the flowers would have a larger and a smaller layer of leather. I looked up painting leather and discovered you can just use acrylic paint. It just takes a few coats, and you have to water it down at first so it doesn't crack.
The person who will be receiving the headband likes fiery orange, but I wasn't sure if I'd choose the right shade... so I opted to do shaded flowers. I think they look better than a flat color would. I mixed up some reddish orange and started painting the larger flower sections, then added some more yellow and painted the smaller flower sections. Because I had to apply the paint in thin layers, it was simple to adjust the shading on the flowers. I gradually added a bit of black and some more red to the outer edges of the bottom flower pieces, and added more and more yellow to the centers. Leather can be shaped when it's wet, and it was certainly wet from the watered down acrylic. I took advantage of this and gently pushed my thumb into the middle of each flower section, pulling the edges toward me to make them slightly cupped. I reshaped them this way with each new coat of paint. I didn't let the paint fully dry between coats because some instructions somewhere online said not to. I have no idea if this actually makes a difference, especially with small flowers. Once the paint was thick enough that the original color of the leather wasn't showing, I added some little dots to the flowers with undiluted acrylic paint.
I then painted some wooden beads orange. They were reddish orange on one side and yellowish orange on the other, continuing with my shading of the flowers.
Once everything was completely dry, I poked holes in the flowers with a sharp thumbtack. There was no way I could push my needle through that leather otherwise without somehow impaling myself. I sewed the flowers together as I sewed them onto the headband one by one. I poked the needle through the larger flower section first, then the smaller one, then a wooden bead with the redder side against the flower, then a tiny seed bead to hold tension on the strong thread. I had to use a thin needle to get through the seed bead. I then poked the needle back down through the wooden bead and leather flower, then stitched it to the headband. Every so often, I put the headband on a styrofoam head to check placement of the flowers (since I couldn't easily imagine where they'd sit on the head).
I made a couple small pieces of iridescent material (the same way I did in my iridescent butterfly hair clip instructable) to go with the teal kid leather. I then cut small leaves from the leather and iridescent stuff. The kid leather was thin and I figured it would weaken it to poke lots of holes down the middle. I used embroidery floss, gluing it down the center of the leaf with fabric glue (I don't think the bond would be strong enough if it didn't span the length of the leaf), tying it around some of the stitching in the headband, then gluing the other end to another leaf. This also took awhile.
I do like the end result, though.