A suggestion, people going on their day to day are busy. So if someone stops them, it is annoying. People on their free time, enjoying themselves usually are relaxed and would mind less being interrupted. So before you approach, ask yourself if someone interrupted me doing “this”, would I be annoyed/angry? the answer would probably the same for women.

Example, if you are playing a videogame, the correct moment would be when you finish or between matches. If you approach on the middle it is annoying/bad manners. If a woman is commuting, it is a bad time. At a bar or social event is fine. At least if you take the polite excuses that mean she is not interested the first time. Which some men refuse to take because they “don’t take no for an answer”.

Basically the rules to approach women are similar to the rules to approach extranger men. We are not that different. The real problem is that some people take advantage of what is called “captive audience”. Example: a salesman in a plain (I’ve seen this and is hell). Approaching a woman at a plane is just as bad because she can’t get away. Pick up artist recommend just that. Or a train, underground, public transport. And this is exactly the problem. Instead of looking for places where people are socializing, they interrupt their day to day and look for places where chances are they are taking their time at a bad moment so they get pressured to give a number just to get away and finish an unwanted conversation.

By the way, this is a mix of common sense and pragmatism, since pressuring people might backfire and approaching relaxed/happy people have more chances to work, sames as selling something.