Here is the proper and absolutely best way to mark a dart. I don’t actually know if it’s the best, but it’s what I do and it works for me.
Start by cutting out the fabric according to the pattern.
On the outer edges of the dart, mark by snipping the fabric IN THE SEAM ALLOWANCE. If you snip past the seam allowance Cordelia will pop out of nowhere and smack you on the back of the left ear. Just Kidding, but you will have problems later on, so just say no to snipping too far.
Now take a pin and poke it through the pattern and fabric at the dart tip.
Fold your top layer of fabric back keeping the pin in place.
Use a marking pen to mark on both pieces where the pin has gone through the fabric. I'm marking the WRONG side of the fabric cause this will help you later on.
Now unpin the two pieces from each other. Using a straight edge draw a line from the dart tip to the outer edge.
Repeat for the other side.
You have just successfully marked a dart!
Tomorrow I will show you how to sew it!
~Melisa & Cordelia