Google images: female preflowers
As you can see on some of those, between the main stem and the new growth coming from the node, you should see some little pinhead sized growths. At first female and male look very similar, but a few days after they are first seen, the female preflowers will be more elongated and there will only be two at each node, one on either side of the new growth. Males will be rounder, almost ball shaped and after a couple days there will be two-four or more grouped together.
They may be hard to distinguish at first, just be patient. They will become obvious after a few days, and far before the time that any males can hurt your females.
Here's a pic of a male, probably ten days or so after the preflowers were first visible:
and another
