This isn't a golden rule as there can be exceptions, but usually you will see a leaf element tip that has a curve on one side and an S-curve on the other. This makes for a very attractive leaf. Quite often the fledgling designer does a double S-curve and the results are often less desirable.
The S-curve can go on the top or the bottom as shown in the illustration bottom right. Sometimes it works better one way than the other.
The double S-curve almost always works on a symmetrical leaf.
The double curve also works in many cases.
I hope these examples help. It's often the little things that can make a noticeable difference and improvement.
