Hey, do you all know how to pivot a dart? It's super easy and fun. Remember my stripey dress, where I pivoted the dart to the center front seam to create a chevron effect?
Here's a miniature of the original pattern piece. (It's actually just a hand drawn piece, so don't look at it for accuracy!) It's best to do this with the seam allowances removed. This way the seam allowance will not interfere with your drafting.
See how the waist dart closes to form a three dimensional shape?
Start by putting your pattern piece on top of a new, clean piece of paper. Make sure you have your apex marked. Update: the bust apex isn't necessarily the end point of the dart, since darts usually stop short of the apex of the bust. In patternmaking, you usually work with a dart that ends at the apex and then, once the dart pivoting is complete, shorten the legs by about 1/2" to 1" so the dart doesn't end right on top of the bust, creating a pointy effect. Check your pattern (fold the darts and hold it up to your body) to make sure that you're working from the apex, which is the fullest point of the bust.
Now, mark your new dart placement. The red arrow indicates where I want my new dart to be. It will radiate diagonally to the bust apex.
Start tracing at the left leg of your old dart. I'm using a green Sharpie here. Continue in a clockwise direction, until you get to your new dart placement point.
Use a ruler to draw new dart legs, connecting them to the apex point.
There you have it! Next you should add seam allowances back. Update: you will also need to shorten the dart by about 1/2" to 1" so the endpoint isn't right on top of the bust. Close up the dart and trace over it with a spiky wheel to get the shape of the seam allowance on the dart body. Straighten up any lines that might have gotten wonky, like the waistline (where the old dart used to be).
Make sense? You can move your dart anywhere: neckline, shoulder seam, French dart. As long as it radiates toward the apex, you're good.
If this is hard to visualize, I would suggest having a go of it with a bit of paper shaped like a pattern piece. It will make sense once you've tried it, I promise.
Let me know if you have questions!