Note: This post is primarily about males looking to be better at talking to females.
Here is the best advice I can give you. I have been there before, read books on how to talk to people, etc. Been there. Those things don't help that much really (sometimes you will come up with an unusual gem though so I guess it is worth it).
First, find a friend, or pay more attention to one of your friends who is funny/sarcastic/good at talking to women (but also a good person). Listen carefully to how this person talks to women or anyone else. The key is to be able to get yourself into a certain state of mind. Learning specific things to say etc is not important. When you have the right attitude/state of mine, everything will flow naturally from that. With the right attitude, you can say ridiculous things, and get away with it. They will think, "Oh he is just being sarcastic." But you need a good model of what this is so you can get it. Try to emulate this state of mind when you meet someone that has it. It is basically an attitude of what fun can I have in this situation? It is also an attitude of not afraid to be sarcastic in a funny way. It is an attitude of not giving too much of a **** about what people think.
Another thing that has been amazingly successful for me is think of all girls you meet as not prospects, but just like any of your friends. Treat them like you would one of your friends. This takes all the pressure off, and paradoxically makes you more attractive because you will seem so much more confident and not trying to get somewhere with them. Basically, not desperate. This doesn't mean you wouldn't be open to the possibility of something more. Basically, go in with no expectations, and be OK with whatever happens.
Learn how to be relaxed even in high pressure situations. Just let go. Things will happen the way they will, even if you are anxious/tense.
So, the things I highly recommend are:
1. Find a mentor/model of the funny/good at talking to girls person. Pay attention an try to model this person's attitude most of all.
2. Treat even women who would intimidate you as just friends. Paradoxically, this will make you more attractive, because you seem to be more confident. And this doesn't mean you aren't open to more. Just be frank.
3. Learn to relax in all situations, physically and mentally. There are many ways of learning to relax (many techniques, etc). If you need info on this, feel free to msg me.
Be spontaneous. Whatever happens, even if bad, think "this should be interesting
". And be respectful of people! Enjoy the ride!