As soon as you approach the girl for the first time. Let me know how that works.
No just kidding dude, but seriously. Let's say you're out on a date, you start out with lots of kino, teasing her a bit, making lots of jokes. Be really flirty, and something amazing will happen. You should start to notice she will become very comfortable in your presence. After you can tell she's comfy, she'll start to be the one to initiate the kino and stuff, this shows she's interested. I usually go in for the kiss whenever there is a silence in the conversation. Then, you can either just go in for the kiss, or say something like "I'm going to kiss you."
This works at any part of the date, preferrably the first date, you may end up making it awkward if you let it linger for too long. Pay attention to her body language and stuff, you can usually tell when the girl wants a kiss. I noticed a girl wanted a kiss from just the way she was looking at me. Or when you go to take the girl home after the date. When the girl tries to stall you, as in her delaying to leave you, or tries to start up a conversation when you're about to leave, that usually means she wants something before the date ends, and most of the time, they want kissed.