i've heard you want it warm not dark. i've also heard it's genetic and doesn't matter. everyone's got an opinion, i've even spouted out many of my own. on this one, i don't even know any more... used to think it was all genetic, but with recent personal research...
if it isn't locked in genetically to begin with, than i believe warmer environments will yield more females, this is based on nothing more than me popping off seed packs in cooler environments and getting mostly males.
but like i said, i don't really know. it seems to be a highly debated issue though