Make time to spend with one another in the evening, watch a movie together, or
have a glass of wine, listen to some music and dance a little in the middle of the living room floor (My favorite

)
You could, every once in a while, get her a card.
Read through them until you find one that matches the both of you perfectly.
She'll know that you were thinking about her and took the time to show it by
reading through some cards until finding the perfect one.
Put it some place where you'll know she'll find it.
Ask her how her day was and really seem interested when she tells you.
Every once in a while, take it upon yourself to stop by the food store on your
way home to pick up some food for you to make a nice family dinner.
And when you say "I love you" say it like you mean it.
Say it often, at least say it every time you leave the house and
when you come home.