Take what I say here with a grain of salt, since I personally think I suck at dialogue but people say it feels natural. I’m just passing on what I have read before.
A common technique to make dialogue more natural is to say it out loud. I would advise doing this somewhere private to prevent odd looks. When you say it out loud, as if acting out a scene with yourself, you’ll automatically change the wording and how you say it to be more ‘natural’. It’ll give you a good feel for your characters, too.
Another thing you can do is observe people talking in real life. A lot of writers do this thing called ‘people watching’. It’s like bird watching, but you watch people instead, trying to discern their behaviour and the way they speak. This’ll teach you how real people speak, how everyone has different speech patterns, and other things. You can also watch movies and tv shows, but they’re rarely as good as real life.
Other than that, just keep practicing and keep getting feedback! You’ll get there <3