Don't let your woman get complacent about sex. You need to keep challenging her. Push her to her limits - and then further.
For example ,tell her you're going to select a random stranger that she has to have sex with. And that you will decide what sex consists of. I recommend telling her she has to give this guy reverse cowgirl sex. That position is always a great performance for the man. This is doubly great:
1) She will be awkward, embarrased, uncomfortable, resentful about being made to have sex with this guy she's never seen before ... but on top of that 2) you insist she does it in a position which amounts to putting on a private sex show for him.
IMPORTANT! Don't give her any choice. She's doing this.