This is how I was taught in order to keep the seam allowance correct. The blue painters tape works real well.

Here's something that I use. I take a 1/2 of stack of post-it-notes and line it up like 1 1/2" before my foot at the 1/4" mark and my pieces go to the needle at a 1/4". If you are considering machine quilting and not just piecing, then I would suggest you purchase a walking foot. This will make quilting the quilt much easier.

To clarify what others have said, a walking foot (even feed foot) will make only straightline (machine guided) quilting easier by allowing the three layers to pass under the presser foot without dragging. To be able to quilt anything with curves (free-motion quilting), you will need a darning foot (sometimes called a hopping foot) and a way to lower or cover the feed dogs.