Now that your pattern is nicely laid out and pinned to the fabric it's time to take a deep breath and cut! No going back now!
First, take a moment to look over your layout before cutting. Are all of your pieces perfectly on grain? Are you missing anything? All the pieces facing the right way? If so, great, let's go!
Although I normally use a rotary cutter, for this pattern I pulled out my trusty scissors just to ensure I still knew how to use them. It was also a good reminder for why I prefer my rotary cutter. Make sure you're using nice sharp scissors reserved for cutting fabric. If your scissors have nicks and rough edges they can snag your fabric and ruin it before you have a chance to use it. I've written "Sewing Scissors DO NOT USE" all over mine to help tell them apart from our regular scissors.
Start with a long, mostly straight edge (the hemline is good) and cut with long, clean, controlled strokes. Don't hurry! Cut on the OUTSIDE of the black cutting line. Again, go slow, there's no reason to rush. Enjoy the cutting process and the sound of the scissors. Be careful not to lift the fabric up any more than is necessary to fit the bottom blade under it. This is one of the many reasons I love my rotary cutter - no lifting of the fabric. However the mats and blades are relatively expensive so most beginners have to serve some time cutting out their patterns the way their grandmothers did. It builds character.
When you get to a corner (such as when you move from cutting the hem to the side seam) cut a little past the turn then come back and start cutting up the side. This helps keep everything neat and sharp.
When you're cutting along a curve, especially a sharper one like you find at the neckline, continue with the long cuts but pivoting the scissors as you cut to follow the curve. What you DON'T want to do is take little snips. It's far too easy for those to turn out a jagged edge.
After the piece is cut out take the time to mark it then and there. (Lesson on marking coming soon.) After marking the piece, leave it there if possible and move on to the next piece. Picking it up can shift the fabric and mean a minute or two of resmoothing before cutting the next piece. Unfortunately my cutting space is so small that I can only cut one large piece at a time so I do pick up just cut pieces, fold them a time or two, and put them in a neat pile off to the side. Basically, do what works for you but do it knowing the reasons and (potential) consequences.
Continue cutting out the various pieces until you're finished. Now take a moment and look over the instruction sheet to make sure you've got everything you need. More than once I've thought I was finished when I'd only cut out one sleeve or forgotten a facing or some other thing like that. Double checking can cut down on a lot of frustration. Now you're ready to sew!