The Shoulder Squeeze
A good way to get the ball rolling is the shoulder squeeze.
Wait until she's not paying attention and then excuse yourself. As you excuse yourself give her a gentle squeeze on the shoulder then trail your fingers down her arm a little (no further than the top of her bicep) as you finish what you're saying.
Example: "Hey Jen, *shoulder squeeze* I'm going to get a fresh drink, *trail off into a gesture of where you're going* would you like anything while I'm up?"
This is just an "I'm getting your attention" touch. It's the equivalent to a backslap among guys and just sends the message that you're a tactile person.
If she looks at you and smiles and responds, give her another squeeze as you leave. When you get back, approach from the other direction and give her other shoulder a light touch to let her know you've arrived.
Sit down and start talking again, when you want to emphasize a point or the two of you are laughing, take her hand in yours and give it another squeeze or a light touch.
She'll start reflecting your actions after the first time you touch her hands. If she draws back when you touch her, at any point, stop making physical advances and just put your hands or body where she can easily reach you. Once she gets comfortable she'll start touching you.
You'll get one hell of a grin out of this once you get comfortable with the thousands of ways people touch one another. Once you start you'll find you've opened the floodgates.
I think women communicate more, better and deeper with their bodies than any other way.
Start pressing those buttons!