Here's some FREE advice from a happily married man!
A) Don't lie.
B) Actually try to listen to what she's saying.
Works like a charm.
C) Lots of compliments. (i.e. You look beautiful today, is that a new sweater?)
Lots of UNEXPECTED compliments. Make her fish for them, then don't give them when she expects them; then when she's about to claw your eyes out, you hit her with the fact you think she's the most angelic creature to grace the sands of this Earth and that you'd be a fool to think you were anything other than blessed.
Oh, shit. I just gave out my secret.