Here's what I do:
I pin vertically to match the points.
I hold on as tight as I can, remove the pin and place into the sewing machine.
Insert the machine needle a bit to the right and a bit before where there are matching points.
Increase your stitch length (just in case you have to rip out)
Sew to a bit after the matching point.
Open and see if the points are matching.
Move on the the next point.
If all points are matching, decrease the stitch length and sew the whole seam.
Does this make sense? It seems to work for me - although my triangles are definitely not perfect, but good enough for me!