While I haven't quite figured out where to put darts on a garment to get the best fit, I did pick up a few little tricks for making nice, neat darts when a pattern calls for it.
Three things make for a great dart. One, the closer you get to the edge of the fabric at the tip of the dart, the smoother the point will be. To accomplish this, I like to sew my darts backwards: from the tip to the wide part. This way, you can set your needle right at the edge and get to work. Otherwise, sew right on up to the edge, and decrease the stitch length to 0.5 mm with about 1/2" to go so that you can be as precise as possible.
Second, the less bulk at the tip the better. This is why many instructions (and your high school home ec teacher) tell you to tie off the end instead of back stitching. But I don't like having threads hanging off, and I also trust my machine more than a hand-done knot. So to secure the stitches, decrease the stitch length to 0.5mm when you are about 1/2" away from the tip (or for the first 1/2" of the tip, if you are sewing from the tip down like me). This will hold that sucker in place, and also allow you to get really close to the edge of the garment if you are sewing from the end to the tip, or if you are doing a double dart.
Lastly, steam the hell out of it. Nice and hot. And because a dart is meant to add some curve to your garment, press it over a curved edge. If you don't have a pressing ham (I don't, but I'm thinking about getting one), you can press it over a bunched up towel.
Check out the tutorial on Burda Style.