Interesting worlds are a plus for me, probably because I'm a bit of a sci-fi fantasy buff. I get much more enthralled by the stories about the tickle wizards, the kinky alien/fantasy races, and the ancient tickle wars than I am with the stories about the guy who tickles his girlfriend upstairs in his apartment.
I also like it when it's not just about tickling. It's pretty fun when tickling is used as a device to move the story forward, rather than as the end-all be-all off the whole story. One sign of stories like this, is when it does not actually end the moment the tickling is done. Still, since this is tickling fiction, I sometimes like to end with tickling as a little punch-line at the end, after the main event, perhaps with a playful tickle attack between friends, or with someone receiving a ticklish comeuppance for something she did earlier in the story.
During the tickling scenes, a sense of change or progress is important. As others have said, you want to try and be as vivid as possible. Describe how the ticklee looks, how the ticklee reacts to being tickled, and how exactly the ticklee is being ticked. Change things up with banter or dialogue. Remember that the ticklee is a character, and should have his or her own special way of reacting to tickling. Also, if the story is not just about tickling, feel free to use their exchanges for the sake of exposition, world-building, character building, or just to move the plot forward.