The overwhelming fault in dialogue from many newer writers is dialogue that doesn't sound genuine. It's just not how real people in the real world talk. -"Writing With A Natural Voice," Larry Brooks, Writer's Digest Mar/Apr 2012
Dialog is NOT a place to info dump.
Dialog should sound like a REAL conversation, not the witty, fabulous remarks you've carefully crafted in your head. (We all know that we never think of that great comeback on the spot . . .)
You should READ your dialogue OUT LOUD and listen to what it really sounds like, off the page.
Dialogue is hard. It just is.
Brooks goes on to suggest sitting down somewhere and listening to people talk around you. Record it. Take notes. Figure out how people's conversations happen in real life.
And on that note, good luck.