Keep it natural and true to the character's personality. Make the dialog flow smoothly and sound like something real people would say.
To write good dialog in a novel, you need to know your characters well. Understand their motives and emotions. Also, vary the length and tone of the dialog to make it interesting. Avoid making it too long or too complicated.
First, make the dialog relevant to the plot and character development. Second, use contractions and informal language to make it seem more realistic. And finally, pay attention to the rhythm and pacing of the dialog to keep the reader engaged.