First trick to starting something with a woman is find someone you are attracted to. I have found it harder to make out with a gal I wasn't overly attracted to than guys, not sure why. Then one day say "have you ever wondered what it would be like to kiss a girl?", preferably after making sure they aren't homophobic. It doesn't take much from there.
If that is still too much 'planning' then it's never going to happen for you. Girls don't just look into another girls eyes and decide to kiss them. They may want to but they won't unless they've gotten confirmation they are not going to be rejected.
'People are never perfect but love can be. People waste time looking for the perfect lover rather than creating the perfect love' - Princess Leigh-Cheri from Still Life With Woodpecker.