If it doesn’t sound like something you or your friends would say in real life, then it will probably sound like two manikins trying to converse? You can try accents and so forth latter on when you’ve mastered simple dialogue. Listen to what people say, and then practice the cadence of what they say in your head. You’ll be surprised at how well this works. I don’t write dialogue the way I talk, because I can’t speak very well, or let’s say it’s a struggle. But I do know how to project a character into dialogue that I write.
It’s kind of like riding a wave. The first few times you get on the board you’re bound to flop into the water. In your writing, after a while, you can ride the wave of dialogue in your head all the way to a cool conversation on the page. You’ll know when you’ve found that place in your head, and you’ll say “Hey, I’m cool.” Don’t get cocky though, because it doesn’t necessarily make you an excellent conversationalist in real life, but your stuff will certainly read better.
eg. From my screenplay The Buried Moon.
INT. BEDROOM – MORNING
A child is waking up in the morning. She gets up dragging her stuffed bunny with her and she gets into bed with her mother and father, crawling over her mother to get in between them. The mother wakes up.
MOMMY What’s the matter sweetheart, bad dream?
SAL Mommy, is the moon really a girl?
MOMMY I always thought it was the man in the moon. Why?
SAL Because she visited me last night, and said that she was in trouble and that probably I was the only one who could help her.
The mother looks worried.
MOMMY Another visitation. Are you sure it wasn’t just a dream.
SAL No, see, she gave me a moon rock.
She holds out a white opalescent rock for her mother to see. The mother takes it from her out stretched hand and looks it over.
MOMMY Where did you get this?
SAL From the moon silly.
MOMMY Sal, you know what I told you about exaggerating, it’s the same as a lying.
SAL But I’m not lying.
MOMMY I think you should go to your room and think about it.
SAL She told me to keep the rock a secret, now how will I find her.
SAL You’re mean.