I was leaving the answer to someone else for a bit but since no one answered I will say how I have come to be a good listener.
I think first of all you must have a compassion for the speaker...any speaker and put yourself in their position, if you were the one talking to (you) would you want to see a person who was just waiting for you to hurry up and finish speaking or would you want to see genuine interest and attention to the talk?
I will always use the technique when I find my mind trying to wonder and if the person is telling me something thay have already told before that is easy to do. Lots of people repeat themselves and it gets harder to listen again and again. So I have adopted a thing (system of better listening skills) where I tell them they already told me... but I do it very, very kindly with a soft voice and with a smile, and maybe a touch to say, no problem, but then they might move on to something new which is easier to listen to....old storys are hard to focus on again and again...so the mind tends to go somewhere else.
Most of all if it is someone I find boring i think that maybe I am the therapy for the person...that they just have a great need to express and I act as a good doctor would and try to pay attention because we all need someone to talk to as the world can be very cold sometimes.
To pay attention to what they are saying is a gift of your time but if you are not really there for them you are not really giving so....they will feel that on some level, know this, and decide if you will tell them something like ..."sorry I am a little bit caught up in my own thoughts/problems right now...but I will try to listen to you better"...then maybe they will want to hear more about you and the conversation will become one you are engaged in, more fully...maybe?
I love people very very much and this makes it easy for me to be interested in what they have to say, some folks may have to work harder than I do to concentrate on the person who is speaking but people have always been there for me so I am happy to be there for people too when they need me. I keep in mind how many others I may have bored... with my conversations too. That helps as well.
I hope this has helped a little. Others sholud add to this thread it is a very good question.