I admit that I've tried my best to create something understandable, but my sewing skills are very amateur and seems like I'm not very good at writing tutorials too ^_^
But I didn't wanted to disappoint my readers, so I searched the web for an easy rectangle skirt tutorial.
I found this one by Dolly Outiftters very easy to understand, plus it's already doll-sized (it's more difficult to start from human clothes patterns).
Anyway if you want to sew a skirt for Mosnter High dolls, you'll need to modify the patter a little: in fact Monster High dolls have a greater waist/hips ratio than the doll used in the tutorial so, if you want your skirt to be poofy enough you have to measure 2 times and a half the hips circumference of your MH and use this measurement for the widest side of the fabric rectangle (side B in my drawing below). Side A is up to your choice: if you want a knee lenght skirt, 8cm are enough.
Since MH dolls are quite small you can also use instead of fabric a piece of tall satin ribbon (as I did for Operetta's skirt) and save some sewing, since ribbon won't fray on the upper and lower side (B), so you'll only have to sew hems on the shorter sides (A).
The last thing you have to consider when sewing for MH is to get the tiniest elastic band you can find (I used a 4mm tall band) or else you'll skirt will end up having a huge waist in proportion to your doll. For the lenght of the waistband don't use the exact waist circumference of the doll, I usually measure 1 time the doll's hips circumference minus a cm: this way the skirt will be reasonably tight on the waist to look nice and the elastic band doesn't stretch too much when sliding over the hips.
If you want to see another example of this pattern on MH dolls, here's another skirt I made using it (again for Operetta, she's one of my favourites!)
I hope my instructions were clear enough, if not or if you still have some doubts feel free to ask ;)
