I learned at a workshop recently, that if I square my material on the selvage edge and not across before I cut my strips...cutting them lengthwise...that the triangles are less stretchy. I've started doing it for all my piecing and the blocks are much sturdier and easier to work with.
I've started a double wedding ring and the trick is to put the larger piece on top. If you have your beginning, middle, and ending points marked on each piece, and don't vary from the quarter inch seam allowance, it eases together without any problem. I do go real slow but I like the results so it's worth it.