I would like to recommend a good book and accompanying DVD. "Mastering Precision Piecing" by Sally Collins. I ... and a few others here on the board call this book the "primer". Her methods will teach you how to concentrate on getting accurate seams starting with cutting, pinning, sewing and pressing.
the amazon link below should pull up a search that will show both the book and the DVD.
http://www.amazon.com/s/ref=nb_sb_ss...n+%2Caps%2C234