Has your teacher asked you to write a dialogue for an English assignment? Are you writing a play? Right now I'm in rehearsal for a show. It's mostly singing and dancing, but I'm in the acting part that connects the numbers. Someone wrote a script, but at the first rehearsal some of it didn't sound as good as it looked on the page. So the writer made a few changes. We used them. Then I made a few changes. Then a couple of the directors made some changes. As we performed the piece we all added bits and pieces that felt right and then wrote them into the script. I was asked to write the final script and send it to the cast. I did. Then another member of the cast made some suggestions. I thought a few of them would work well and I made yet more changes. You might be muttering to yourself, 'Why is she telling us this?'
If you are writing dialogue you have to say it out loud to the room, to the computer, as you walk home from the bus stop, or read your script on the bus (pen in hand). It's organic. It grows and changes. Some things work well on the page, and sometimes even when you read them out loud. But they don't always work if you are acting them on a stage. So if you are writing a play, or a page of dialogue, read and act it until if feels 'real.'
My show is June 3rd, so I'll get back to you. Watch this space.