I love Trudy from HotPatterns. They have some great stuff, a nice selection of patterns and often a free one you can download from Fabric.com.
Here's her latest tutorial, and I think it's invaluable. She has some refinements on lengthening a t-shirt pattern into a dress, and also some tips on going from sleeves to sleeveless.
Also, check out the very cool dress she's wearing. I told her I think it would also look fabulous chopped up even more, maybe twice more down the front. And you know, Trudy is all about fabulous.
Enjoy -- hope you learn as much as I did!