Step 1. Choose a good skirt to work with. This particular technique works best with wool-like skirts. If this is your first time for hemming a skirt, look for one that is unlined and straighter vs. fuller. The less material, the easier it will be to work with. Also look at the existing hem. If it is a blind hem, then you know that a shorter length with a blind hem will work well. Don't forget to take your before photo!
Step 2. Try on the skirt and mark the length that you would like it to be with a straight pin. You could also measure off of a skirt you already own that you know will be a good length. I usually shoot for finger-tip length, then I know it will be appropriate for school. If this is your first time shortening a skirt, I would aim for the conservative side. You can always go shorter later, but you can't add length back on.
Step 3. Take off the skirt and measure down to the hem to get the length that you need to remove. In my case, it is 11.25 inches
Step 8. Start cutting across the front of the skirt. Getting as close as possible to the pins. Repeat the pinning and cutting process on the back.
Step 11. Now the tricky part, folding it properly for the blind hem. Lay the skirt with the wrong side facing up. Fold the hem underneath so that there is 1/4 inch of the edge exposed. Repin.
Step 13. Once you've sewn a blind hem all the way around, be sure to iron your new hem. It will be a nice finishing touch. Finally, take your after photo and show off your handiwork to all your friends.
All right, that's it. My first tutorial. Hopefully I was clear enough in all my instructions. If you have any questions, be sure to let me know.
Edit: If you hem a skirt using this tutorial, be sure to let me know. I want to see photos!