This one is a little bit advanced but:

Vogue puts out these really great fitting patterns- basic shapes from which you can develop a very accurate block for yourself or for someone who might want you to make them a little something. Along with the paper pattern, detailed instructions are included addressing measurements, general pattern drafting and sewing techniques.

Grab the size that more or less fits your particular measurements, read through and follow all of the steps then make a quick mock up before getting down and designing- using an inexpensive medium weight woven, non stretch, stripe or plaid/check will show any fitting flaws.

A little bit pricy at $27.50 per envelope, however, Fabricland (www.fabricland.com) sells Vogue patterns at 50% off as far back as I can remember; pattern #1003 for pants and #1004 for a bodice and skirt.