This is not a task for the faint-hearted! Although it is really easy to do, just handling large amounts of fabric can be a nightmare.
I had a pair of curtains that were way too long for the window and because the radiator is under the window when they were drawn they cut out all the heat so I thought I would just reduce the length. I ended up decorating them too! Instructions for this can be found on my blog Nursery Makeover #1 Curtains.
Rotary Cutter and Cutting mat
Chalk or fabric pen
Wonderweb or similar iron on hemming tape
How to Do It
First measure the window and decide how long you'd like your curtains. Add enough for a decent sized hem. At least 4cm.
Lay the curtains on a work surface. I used my dining room table.
Using a ruler, rotary cutter and mat cut along the line.
Place onto ironing table and fold over the hem. Press with the steam iron.
Fold the raw edge in, measure the hem allowance and press again.
Cut the wonderweb the same length as the width of the curtains. I used 2 pieces because I wanted a deep hem. Lay the wonderweb along the hem and press.