A true way to get a sense of dialogue is to pay attention to what is being said and what you are saying all day. This will be a two part homework assignment.
1. You need to write down everything you say all day long. This means from the time you wake-up to the time you go to bed. Now if you are in a profession that you are talking all day long or what you say is confidential, you can make up rules for yourself.
For example, a teacher would not write down when he/she was teaching a lesson, but his/her rule would be to write the informal communication he/she would have. He/she would write down the hellos and good-byes that he/she shares with students, greeting people in the hallway, etc. He/she would also write down conversations with other teachers, the coffee shop cashier, and with his/her husband or wife.
Every writer should at least do this once in his/her life, and multiple times if able. Bring a tablet, paper, or sticky notes around with you all day. Another option is to tape record the day, but the trick is to transcribe it. It is important to see it written.
Do this one day, and let me know how it worked out.
2. Write down what others say. Sit in a cafe, in a hair salon, at the registry of motor vehicles, bus stop, subway station, etc, and write down what others are saying. I have had great story ideas just from a sentence that someone has said as they walked by me. This requires some stealth. I know it is tempting don't grab your stenotype. You need to be on stealth mode.
Let me know how all of these pan out again. I plan to write down what I say in a day in the next few days. Stay tuned!