After several trials and errors, I am sharing my opinion on how to approach a girl and how to talk with her, in direct and natural way without routines, false time constraint and so on.
First, you have to be ready and you should read about body language and your dress style.
[The following method works for me. Of course, sometimes I am also using the Mystery Method].
So, you see a woman you like, sitting with her friend. You need to approach them before they see you. That is, if you are going to need some time to think about it, do it away where they can't see that you are afraid.
Approach them from the front. Avoid to approach them from the side, where they can't see you approaching, because you will get some bad impression. Before you are close to them, smile and look at them in the eyes. With this, they will understand what are you going to do and the smile calms them.
Go straight to your target and say to her that you like her and want to get to know her (or she looks like an interest person and you want to say a hello to her).
Introduce yourself with her and immediately ask for her friend. You can say something "Is she your friend?" and introduce yourself with her.
Immediately give a sincere compliment to her friend, you need her to your side. Do this by telling her that she is wearing something nice or she has a sense of fashion, etc. She will like it (especially if she is a woman who is not getting a lot of compliments) and she will like you too, so she will let you to talk to her friend, without blocks you.
Do not ask the same things in both girls. You should work with your target. If you are asking the same questions to her friend, your target may think that you are a player, or you like her friend or even you don't have something to say.
If you do well, you will have immediate attraction on her. So, you should go to qualification, by asking some personal questions. Without attraction, girls do not answering personal questions to strangers, so you have to win her first.
To help you with the conversation, women gives you anything you need to continue with the conversation. You have to listen to what she is saying and to choose words for further discussion. This makes you look sincere and helps to build a deeper connection with the girl. For example, if she saying something about her "neighborhood", ask her to tell you more about the neighborhood she grew up, if she saying about "dogs", ask her if she has a pet or what pet she likes.
You can build more connection, if you are having some common things. If she is likes you, you can say something like "Really? Wait a minute, we have to stop talking because i am starting to fall in love. I also enjoy this or that".
Note that you should continue to talk about "this" and "that", in order to take her mind from "I'm falling in love" and "we should stop talking" shields women have, so she will not thinking about these, because then she will put a "shield" in front of her.
If you build enough rapport, then you can take her number or ask her if she is going to another bar, etc. The number you will take will not be a "flake", because you already built a genuine connection with her.