Anything spontaneous and exciting should help spice it up some, but make sure you pick an appropriate time. If you've been together for six months, you should be able to mostly tell what his mood is. If he's had a rough day, try giving him a massage and do other things to make him feel nice. Then slowly change the mood to a more sensuous one. But make sure you have his interests in mind. If he makes it blatantly obvious that he isn't in the mood, don't push it. You could try dressing up, too. That's usually fun.
