You can find 'recipes' for making patterns if you search online for Drafting Pattern Blocks.
I have made a skirt block for myself with the fashion-era link that will come top of that search. I'm still scared of the trouser blocks though!
There is a book called Sew What! Skirts which again has detailed instructions on drafting different styles of skirt. I have read good and bad reviews of it but it is probably still worth looking at.
Fast Fit by Sandra Betzina
is a good book to read to help you see where and how to adjust existing patterns to fit you better. Large parts of it are on Google Books but I borrowed a copy from the library.
Lots of sewing blogs have pattern drafting tips and
Just Tutes is only about pattern making, mostly for little people but her ideas can easily be scaled up for adults.