Just ask her things like "how was your day?" And start from there, ask her what her idea is of a perfect date. And if she would want to go out..? Tell her you love her. (:
You can ask your girlfriend a variety of questions as I personally think that an open and also honest relationship is a very committed and once again honest relationship. Then again another question...
All you have to do is ask her what's going on, and if she wants to tell you something. Or one of the oldest that we all use is " I love you and please make time so we can talk for a bit."