Surprised that Ginny actually pressed her lips back to his after the first initial kiss, Draco just acted. George had given him sound advice, on just being honest, and Draco knew as well as the next Slytherin that that meant being honest with your body, too.
As their kiss deepened, Draco allowed himself to drift backward, toward the sofa--even going so far as to trusting Ginny to take control of it. However, he kept the pressure against her lips equal, or more firm, to hers. He had to give her a reason to keep kissing him, after all.