Fabric makes a big difference. When I use a cheap stretchy fabric it is much harder to match seams.
Also when making strip sets I cut them in half so they are the size of a fat quarter length, this helps keep them from getting out of shape. Pressing makes a difference also. I use a small travel iron, it is not heavy so will not distort like a heavy iron. If you do all this you will not need to pin your seams will fit togather just by feel.