I am still not really experienced with this yet but you'll always want alpha's for hair, at least at the tips so it doesn't look as blocky.
Ideally you want to use alpha's to simulate depth and perturb the silhouette of the hair.
You should create a skull cap to give you a starting point.
duplicate the head-mesh and delete all the faces except the ones where you would expect to see hair so you are left with what looks like a form fitting skull cap.
(keep the skullcap for more hair-styles later but remember to use a different skullcap for the girls head.)
I think the skull-cap part should probably always be done but the rest of everything I wrote here can just be improvised,
because I haven't actually made any low-poly long hair yet and everything is only in my brain..... 
move the points of the skull-cap to match the basic hair shape you are going for.
then more obvious things like cutting a hairline (if one exists) can be done or extruding some of the surrounding edges to make long hair...
at some point you will almost certaintly be adding hair "chunks" (pieces of hair with alpha's)
when you do, it is probably in your best interest to make one hair chunk and duplicate as need be to different area's of the hair, and then modify it later.
Sorry 'bout that, but I noticed that there's a distinct lack of curls in most games. Everyone has long flowing or wavy hair, why not curls, eh? Don't worry if it can't be done though, was just an idle thought of mine. If curls could be done maybe we can have realistic looking afro hairdos as well 
