Cutting: Purchasing a quality rotary cutter and self-healing mat are essential in making a good quilt. If you take the time in the beginning to make sure your squares or triangles are cut straight and are correct, then it makes pieces MUCH easier.
The first quilt I made (see the picture on First Quilt post) I wasn't very careful with cutting the squares. If you look closely, the corners don't really line up and every once in a while you can see a pucker along a seam line. When I pieced the rows together, I tried to make the seams line up as best I could by pinning, so it ended up with excess fabric in between the seams in certain places. It made the piecing and assembly the borders a bit more of a chore than it should have been.
For the baby quilt I'm working on now, I was very careful with cutting and all the pieces lined up perfectly. I still pinned the rows to at the seams to make sure the squares all lined up, but I didn't have any problems sewing it. I don't have a picture of it yet, but I will try to get one posted soon.