Ditto to all of the above, and then: When I need to match up points I put a pin through the intersection of the point of each block to make sure they are in the same place. Then, holding the block together with this pin sticking through it, I pin the rest of the seam. This usually works for me.
I've also read a lot on this board about folks using Elmer's washable school glue to match up seams before sewing.