First get your materials together!
You will need::
1x pair ugg boots/slippers/whatever. I got mine for $8 from Aldi! Hurrah!
Thin note paper + a pen/pencil
Felt of your colour choice
and a needle.
As you can see above, I already have a little stencil made. All I did was google image searched Batman Logo. All I had was red felt, and I knew there was a red logo somewhere. There is, it's a Batman + Robin type thing, but I settled on the Batman Begins logo. I got my thin paper and held it up to the computer monitor and traced over it with my pen. It's fairly symmetrical, so I just folded it in half when I cut it out to make it perfect.
Pin it to your felt and cut it out. I folded my felt in half and cut out half a bat, neatening the edges when I unfolded it.
Now pin them to the back of your boots, making sure they are even. Handstitch the Bats onto the boots. I used an overcast-type stitch. To secure them in place.
THE END! Take photos!