One way that's worked for me is....."you have a great laugh"...this is 9 times out of ten met with "i love to laugh" (maybe one of the most redundant statements in history, but gets you to point b which is) "i bet you'd be a blast to tickle."
Suggest you be on at least "mutuallty understood unspoken sexual tension" status. And don't necessarily tickle then. It's a reconnaisance mission.. Not engaging at this point ;-)
If you're looking to disclose.about you.re own ticklishness this one has worked ....other person mentions some "hilariousl movie, you say you didn't find it funny, "but then again, its tough to make me laugh".....(see where we're going here?) She might say "nothing makes you laugh?"....
Easy enough.to dock the ship from there, Cap'n
Bottom line is just be easy to talk to, be appropriate, pick the right spots and times ...women will confide and flirt if they like and trust.