What I had found helpful is that I sew over the pins. When I first started, I used pins like Patrice showed in her pictures. Then in a quilting class, they told me that if I get IBC silk pins, they're much smaller pins and I can sew over them. I have lost a few pins over the years, but overall this has worked without incident.
I've found that this has been helpful in keeping my seams matched up. Before, I would pin, everything would be perfect, then I would pull out the pin right before it went under the needle, and that was enough to mess up my piecing and get not perfect corners. Whereas now, they pretty much stay in place.
Also, make sure your seams "nest" with each other, where you press them in opposite directions. That makes things a lot easier too.