Women's excitement toward sex is directly linked to how we feel we are perceived. If we feel pretty, sexy, desirable, we will usually enter into a sexual activity with more anticipation. Having a strong emotional base, during non-sexual times will make her feel more loved. Take time to smile at her, tell her she's beautiful;...
Start those 'teasing touches' during the day. Sneak a little butt rub as you pass her in the hall, or wrap your arms around her at the sink, slipping one hand up her blouse. Then back off... just let her ponder the feeling for a while.

A woman's sexual experience often begins long before you get into the bedroom. My husband learned a long time ago that my body doesn't have an 'on/off' button laying next to the bed.
If you have kids, farm them out for a weekend. Or better yet (cuz women always find work to be done at home) check into a hotel. Have several candles ready to be lit, a bottle of wine - and talk. Talk about your lives, your dreams, re-connect to the real person. Listen to her. If the conversation moves in the direction of sex, try to find out what she desires. She may not even know, but at least your letting her know that it's okay for her to have personal sexual desires, even fantasies.
This type of breakthough may take a while, but consider it 'foreplay'. It just may be the best investment of time you have ever made!
Good Luck!