I have heard about guys that are able to persuade a girl to do that. I tried that a few times with quite negative... or rather really negative outcome. Since I do not want to ask women at work, I don't really know were to start... Can someone please help?
The negativity might be for a few different reasons, there's dodgy characters about so they might simply not like the idea just because they're just looking out for their own safety, asking a girl out on the spot like that can make them question your intentions, you have shown interest in a very forth right manner and this can be intimidating to some women.
Some guys find it easier to be straight and up front and do that and some find it easier to go slowly with someone they're fond of, I think the second option works best either way. It's nice for women to know you're interested if you show consistent interest and THEN ask her if she would like coffee, it shows respect for her space and time. Asking a girl immediately without really knowing her might make her feel you're slightly desperate and that would lead her to question your motives and you as a person.
You should go out and socialize. I read a study before that proves the majority of people know each other through work, college or a course they take. Take a language class, play group sports, volunteer, etc...anything that involves the presence of a lot of people.
Yeah, it can work. You're going to get a relatively low response rate, but you can ask a lot of strangers out for coffee, so it can be more effective then slowly making friends then asking one out every couple months. Just keep your head up. She might have a boyfriend, she might not be interested in dating, she might be busy, she might prefer guys different from you, who knows.
As said in another answer, don't just ask out, try to make conversation, flirt, if you get some flirt back, either ask for coffee or ask for her number.
You don't just ask her for a coffee, you see a girl reading a book on a bench just start a conversation, lovely day isn't it? then go from there, but you have to flirt and show clear beyond friend intentions then after like 15 minutes if you've built enough comfort and rapport say
"hey I was actually on my way to get coffee, you interested in a cup?"
I haven't asked out a woman for coffee on the street, but I did pick up a total stranger in the grocery store for drinks later in the week. It's not as crazy or as hard as you might think. You just start with an innocent conversation, gauge her potential interest by whether she wants to engage in conversation with you and by reading her body language as you go along. You don't ask her out unless the signs are positive.