Take a pair of old jeans that fit you round the waist ok.

Cut the legs off to how ever long you want the skirt to be. If you want it to be kind of short, just do what I did and cut off the legs so they look like a pair of shorts

(I already cut the legs off my jeans)

Then pick apart the inside leg seam using a seam ripper.
(Not to worry if you haven't got one... just use a pair of sharp scissors or a pin.)

Just be careful not to stick yourself!

Pick apart the seam in the centre at the front.

Do this all the way up to the bottom of the zip.

You should have something that looks like my picture.

Then you take the centre seam and line it up so it looks straight on the skirt.

Pin and sew this seam using the same coloured thread that's on the rest of your jeans.
I was lucky because my jeans used black thread :)

Then I put the skirt on to see how it sat. I noticed the back centre seam was flicking out a little bit.
This annoyed me.

I took it off and picked the back centre seam apart just a little then sewed it(just like I did with the front seam)

It seamed to work fine and I took some pictures!