So this is probably overkill, but in college I took a class on garment design and construction/pattern making and we used these two books as our textbooks. Again probably way more information than if you just want to learn how to take in some shirts or something, but knowing the fundamentals is of course immensely useful if you wanted to explore this topic further. Also a lot of fun, so I highly recommend learning how to sew for everybody.
http://www.amazon.com/gp/product/0321062841/ http://www.amazon.com/gp/product/1563673290/