I pin first at the intersection of seams and then out to the edges. This (usually) gives me accurate points and if I need to ease/fudge the balance of the seam it's not quite so noticable. I pin straight up/down through the center of both intersections then pin closely on either side of the original pin. If your pin is not happy staying perpendicular to the piece you are pinning, lay your pin along the seam line you want to match to when pinning on either side. This usually keeps things straight. Hopefully that made sense.
Also remember that if you need to 'ease' fabric, put the side with the most fabric on the underside you are sewing - i.e., bunchier fabric to the feed dogs...this will also help ease your fabric. Make sure you pin your ends together where they are supposed to meet. Pull/stretch your fabric as necessary along the way. Steam is your friend when you are pressing after sewing.