I followed patterns when sewing for work till about 4 years ago. The most I ever changed anything was making it wider to fit. I happened across this book, Sewing for Plus Sizes by Barbra Deckert. What a revelation. I have all kinds of sewing books, probably not the best ones on the market, bought at a remainder place as they are, but they are decent. This book, though changed my sewing, my crocheting, and if I ever knit a sweater for myself, my knitting.
The writer discusses plus sizes, from a plus size perspective. She hits all the areas where we plus sized people take issues with standard patterns. She deals with patterns that assume because you are ample, you are tall, amazonian even. She shows clearly how to adjust, change, mangle and rebuild every single fit issue I've come across. She teaches the basics of proportion, design considerations, texture and weight of fabric considerations, so the sewer can be the best she can be. She does tend to speak more of one certain figure type, but I think that is because it is her figure type. Everything I ever wanted in a book on plus sizes, written by someone who is plus size. Darn fine Book.
Oh, and the other very very cool thing? She shows how to make a dress form to fit your body. At home. On your own. At a very low cost. Very very cool.
Whoops, digressed a little again. Where was I? Ah yes. Her book changed my attitude towards fit from 'never going to happen', to OK, let me think about it, and I have been blithely making things fit better in every media ever since. I know what to do to make my sweaters fit so the front doesn't pull up. I understood why Emma's short row concept on the Tubey that Curlerchick is working on will work. (Curlerchick is assisting me learn short rows, and the horrors of wraps!!! Curlerchick has me side listed on her blog!!! Its really not like I'm stalking her, at all. Nuh uhh.)
Of course that doesn't always help. I still need to fix that measuring problem I have, and well follow a pattern? Who me? I turned out a clunker last year, that I intend to fix, if I ever get up the gumption.
So, to make a really long story short, if you find that the sweaters you crochet and knit are not fitting as well as you would like, go get a really good sewing book which discusses pattern alterations and fit issues. Think of your sweater parts as pattern parts, and then apply what you know about short rows, and all the other little knit tricks out there, to make perfect fit yours.
Then go get Lily Chin's masterful Couture Crochet Workshop. Lily completes the circle. Her book shows you how to take your modified pattern and turn the fit into crochet and knitwear, any pattern, any stitch design, and to use the shaping and texture to show off a yarn and your work to its very best advantage.
Sewing for Plus Sizes rates a Double Crochet, a sound solid resource book.
Couture Crochet Workshop rates a Treble.