Snerkablee, you're in luck. The TMF has a thread describing what you're after, called,,,
<I>CONVERSATIONAL TICKLING !!! </I> Learn all about it here...
http://www.ticklingforum.com/showthread.php?threadid=18716
(Okay, that's a shameless self plug, uhmmm, well, it does fit here. Anyway, back to Snerk's problem)
Okay Snerk, here is my <I>general </I> suggestion as to how to move into the matter of conversational tickling for you and your girlfriend at this time in your lives. You will have to fill in the details by yourself for the specific context in which you find yourself and her at this moment.
Whatever, whatever.
Most of us humans like kissing. Take advantage of this fact and kiss your girlfried. Kiss her a lot. (I know this is tough advice, but search for your inner strength and force it.)
Okay, Let the kissing continue, and, with <I>one fingertip </I> (that's <I>one only</I>, don't flood her sensory receptors) slide, glide, and trace a random pattern across her back,,, from shoulders to waistline. Remember the shoulder blades, the spine, and the small of the back, too. Don't miss a single square inch of her back. Slide that fingertip all over it; everywhere.
If this girl hates tickling, you will know this in approximately 5 seconds flat.
If she doesn't respond, you're still probably okay.
Be ready for a 3rd, not too likely possibility: she's one of us, and demands that you give her more, and give it to her right then and there on the spot.
All this assumes, of course, the normal regular polite things that a boy and girl do for each other; e.g., take a shower 2 to 3 hours before meeting the girl, make sure neither of of you are keeping the other one awake too late; and don't allow alocohol or bizzarre foods to affect the setting, etc., etc., etc..
You want yourself and herself <I>both</I> to be alert, sober, clean, and non-distracted for this.
Again, do whatever you need to do to prepare yourself psychologically (and don't ask me how to prepare yourself, make up your own plan) for your girl to give you any one of at least three different possible responses:
[1] Hates it
[2] Doesn't care
[3] Likes it