I know I was very nervous for my first session with a new ler. Because of this I wasn't as ticklish as normal.
The more relaxed I am with the ler the more ticklish I am also. So this is my advice let yourself get as comfortable as possible. If the ler is experienced then they will know what to do to make you more ticklish if you want it. And remember you are the one in charge so if you want the ler to change something make sure you tell them.
Have fun, I look forward to an update on how the session goes.