KISS star Gene Simmons says the best way to survive in rock is to avoid booze and drugs — and concentrate on sex. He told us as he prepared for tonight’s sold-out concert at the Garden: “The only way to do it is no booze, no drugs . . . If you are not clean, you don’t belong up there. I’ve never been drunk or high in my life. The only way to survive the long haul is to be straight-nosed. I’ve been here for four decades.” Simmons, who romanced Cher and Diana Ross before settling with former Playboy Playmate Shannon Tweed, said, “The only temptation I’ve had in my career is of the female variety. And that’s one you can enjoy.”