Get close. Back up.
Add OCF. Try natural light.
Pose. Let them freestyle.

Try everything.

I find myself moving further and further from actual instruction during posing and moving more into conceptual posing. I can tell a person to shift their body weight, move an arm, and even flip their hair but I find it a million times easier to give my subjects a concept and let them execute it. I've found this does a couple of things that I really enjoy:

1) It makes your subject part of your creative process.
Face it. People are paying you to bring the best out of them. Why not use them to bring the best out of themselves?

For the picture below, I told the groom to "press her against the wall and go in for a romantic kiss... but try not to look aggressive". Voila. Here is this "film noir" looking image of a groom going for it. I felt it brought out a lot in this couple. The groom is a 6'4" tall guy so making him appear softer was important to making this image work.

2) It gives the subject freedom.
I'm not a fan of feeling like I'm restricted in what I can and can't do so why would I put that type of pressure on a couple. I want them to feel like they can be themselves without inhibition.

"What does a "normal" day on the couch look like for you guys? Let's capture that."  When you ask for concepts, the subjects no longer feel lost or have that feeling like they may be "posing incorrectly". You're going to look your most natural when you're most comfortable. Letting people be who they are everyday is an easy way to make that happen.

3) It leaves room for the unexpected.
Sometimes you never know what the subject will do.

"Hold her like you normally would at home... wait, you normally hold her with her back towards you??"  There's no way I could have predicted that this would be a most comfortable and natural pose for this couple. Period. Impossible. As a matter of fact, shy of sitting against him in a chair, I'm not sure I'd ever post a couple like this standing up. But here it is. Comfortable and natural and full of real happiness.

 I've had great results with this method and rarely have to make small adjustments for strange things (balled up fists, hair, et al). All of this adds up to a subject that is comfortably revealing their true self and great images. :)