pinning at each (join) is important- often sections go in the same direction- you stick a pin in exactly at a point on one section- then line up the other piece and put the pin in exactly where it needs to be to be lined up-
then when you have them exact you put a pin on each side of the first one to hold the 2 sections in place while sewing- you do this at each point you are trying to line up- then as you sew- sew slowly right on the line (which is lined up perfectly underneath because you pinned well) removing each pin as you get to it-
open it up---perfect block with perfect points/joins :)