I can definitely see this post getting a lot of negative attention. I'm absolutely surprised someone hasn't come on here yet complaining. (Not me personally, but I have seen other posts similar to this "how can I tickle someone..." blasted by "you're so creepy, only tickle with consent" comments)
Honestly, I wouldn't force anything. If it happens it happens. If not, then oh well. For getting them to tickle you, that can be pretty difficult. I'm going to say for the average person, tickling isn't constantly or frequently on the brain like the rest of us. You may see your friends barefoot on the couch and think "tickle" whereas in a reverse situation they think "feet. Gross" or "that spot is taken by his feet", you get it. There's not really one way to "make" someone tickle you short of asking directly. You could try putting your bare feet close to someone, stretching your arms up exposing your underarms, etc. but it's relatively unlikely that a regular person will instantly jump to a tickle. It depends on your dynamic with your friends. If you guys have a goofy, touchy Feely relationship then it's plausible.
As for tickling others, I would start off by analyzing your friendships and thinking about how close you are with this person. Are they going to be weirded out or freaked out if you randomly touch or tickle them? Is your relationship with them close enough that you can get away with tickling them?
Example: I have a completely unticklish best friend who I have known for 12+ years since freshman year of high school. I have been trying to find a tickle spot on her (within reason) for years, once we got comfortable with each other. If we weren't at that level, I'd never try.
Assuming these are close friends, I would just playfully try to tickle them. Poke a side, tickle foot, then tease them if they respond "oh you're ticklish?" Similar to the above poster.
