By Treat them like your male friends, most seductionists mean "don't put her on a pedestal unless you're willing to climb to sit beside her". This does not mean to loudly fart and saw "wow, I'll give it a four since I didn't have any warning it was coming...".
When I am with a platonic female friend, I don't get into the mushy crap of "you look stunning this evening" nor do I buy flowers, jewelry, or anything else that is possibly construed as a play to get in her undies. When she knocks on the door, I tell her "It's open" as I do with male friends. When she looks hot, I do my best to ignore it. (Lesson learned, try to find a female friend with smaller breasts if you like women with bigger breasts, mine drives me up the walls when she wears tight sweaters.)
Otherwise, forget that she is a woman. Treat her as a human, not as a gender. Invite her over, split a six pack (if you are of age). Play cards, Xbox, go out clubbing, shoot some pool, just don't treat her like she is a flower that must be handed like a flower.
No roughhousing, or anything like that. Just avoid both ends of the spectrum.