As far as private play partners go, my only real requirement is that their approach towards play be roughly in the same ballpark as mine. I view tickling as a form of power exchange, and if I'm going to spend my private time playing with someone, I'm not really interested unless they view it rougly the same way. Whether they voluntarily surrender said power in the beginning or decide to fight like hell and turn things into a contest of wills is negotiable, both have their charms (the same philosophy holds true for those occasional times I feel switchy).
With the girl I was most recently dating (well, I've done this with others, but I'm just using the example that's freshest in my head), we generally had a pre-play ritual (our play usually consisted of things other than tickling) where I would basically hypnotize her, for lack of a better word. It just consisted of caressing, manipulation of pressure points, very minor pain via hair pulling and scratching, etc.; but it got her into subspace. An Acquaintance of mine calls it 'the Interview With the Vampire thing'; she called it 'playing dolly', because she said that's what it made her feel like in the sense that I now had total control over her actions and she was sort of an extension of me. To me, it felt like control of the energy field the two of us produced was now completely with me, and that she was basically a puppet, with invisible strings resting in my hands. It's honestly the hottest feeling ever.
To give an example, I was standing behind her, one arm around her waist, the other one very lightly around her throat, and I lowered us both down to the ground with me supporting her still (if I had let go of her at this point, she probably would have fallen over, and that would have ended the mood real quick). Once I got her to her knees, I leaned her forward so she was now on her knees with her forehead touching. Then, more or less on top of her, I took her arms and slid them forward in front of her, with the end position being her on her knees, forehead to the ground, arms completely out in front of her (basically like she was praying). Then I got up, grabbed ahold of her hair, and led her around the living room by it (she was crawling).
Ah, so much fun.