Frankly, if you are approaching a woman who doesn’t know you from Adam, you’d best be amusing and a quick thinker. You might start with an innocuous comment about the weather or wherever you are. Then a compliment about something about her.
If she seems to be a bit receptive (not giving you the cold shoulder), you might press on with a joke, or a more personal question about what she does or why she’s wherever you are. Perhaps even better would be to disclose something about yourself before you ask something of her. You’re looking for an interest in common. Once you find that, you can build on it, and get a number or a date, if that’s what you’re going for. Confidence is crucial for this approach.
If you just want to get laid, I’m told that “Wanna fuck?” usually strikes out, but occasionally gets a hit. You have to approach a lot of strange women, unless, of course, you are famous, a rock star, or really hot. Even then, you won’t get lucky every time.
Ok, that was all so this answer won’t get modded. You have to look like you’re being serious or the overzealous mods will delete the answer even though it follows the rules. The truth is that the above is all bullshit (albeit, plausible bullshit).
The real answer is skillfully using the club and the net. Club her over the head, throw the net over her, and drag her back to your cave. Works like a charm!