Seduction starts long before penetration... take it slow.
One thing I have noticed is that when my GW is having a bad day, a sincere hug (no groping) does wonders for her mood. Then I suggest something odd and funny, like ice cream, or going for a drive, or taking her to a movie (one that SHE wants to see!) or something like that.
And then there are some situations that no matter WHAT you do, nothing helps...
Good luck