Press, press, press, press every seam before you attempt to sew it to the next section. Each section should be pressed in the opposite direction and then you can feel the "hill & valley" when you butt the 2 seams together.
I never pin this area, but I do use a stiletto to hold the seams together until they reach the needle. I use my stiletto much more than pins as I can't seem to sew without one in my hand. (And, it comes in handy if the quilt police get too close!)