Darts take in the fabric below your chest, which is generally larger in circumference than your stomach. Trace the lines to sew together with a pencil, and then pin them together. Sew them, maybe twice if you're para, and when you start / stop make sure you backstitch a bit to make sure it's strong (and doesn't come apart when you've had a lot to eat at that great dinner and need to hold your bulging stomach in. yum.)
Go ahead and sew the darts for both the front outer pieces, and the fleece lining. I did it later, but you might as well while you're in a darty mood.