My character dialog is the best part of my novellas. By "best," I mean it's the least terrible part. What I'm trying to say is that I know where my strengths lie.
The how is in the editing. I make about three passes of rewriting each scene. These are not just proofreads for typos but serious rewrites in which all material is potentially on the chopping block. With each paragraph, I ask myself questions like these. "Can this dialog be more emotionally impactful? Can this line serve more than one purpose? Are there shorter ways to say this so the paragraph scene is tighter? Is this character's voice distinct enough? How do I make this gag punchier?"
I can provide a work-in-progress example from my current episode of an old story that I'm updating. I can if anyone is interested. I think I got the point across though.
Sometimes the most efficient way of saying something is to not say it at all. I trust my audience to fill in some blanks. Like @silverjackie1wrote, a silent comic can be powerful.