Tickling is interesting in that it's something that one can't do to themselves -- you almost always need someone else to do engage in it, in order to create that unexpected reaction/"tickled" response.
I think it's one of those fetishes that originates from childhood. Almost all of us have experienced a scenario where maybe another kid (or kids) held us down and tickled us. Tickling sessions seem to work best when combined with restraint of some kind. I personally love the 1,2 combo of packaging wrap (like saran wrap) mummification and then cutting holes in the saran wrap to tickle.
The biggest challenges are making sure that the victim, err, play partner doesn't get injured when trying to squirm away. A lot of opportunities for them to fall off of surfaces. Maybe consider playing with them already on the ground, away from sharp edges of furniture, and so forth.
Also, you are essentially giving your play partner a hardcore abs workout when you do a tickling scene. Be conscious of the fact that their sides will literally hurt from laughter when they're done.
When you pre-negotiate, does your play partner want humiliation with tickling (e.g., tickle them until they pee themselves, making fun of a manly-man for squealing like a little girl, etc.)? You can also do the 0 to 10 "pain scale" and ask them for a number from time to time, so see if they're about to "yellow".
It's extremely interesting to me that I've met a large number of heavy bottoms and masochists, and tickle torture is often one form of play they won't allow as a "hard limit". I think that, in some ways, tickling involves more surrendering of control than almost any other form of BDSM play.
Have fun
