1) start a new paragraph every time a different character thinks, does something or speaks. 

2) make it seem real. things people do in real life: 

laugh at their own jokes;

trailing off and not finishing a sentence;

interrupt a line of thought with a new one;

say 'uh' or 'um' when unsure;

accidentally blend words together (kinda, gotta, lotta);

repeat words, 'like' or 'literally';

fizzing words out when they realise no one is listening;

use hand gestures, wild facial expressions, random noises and movements when explaining something.

3) give the dialogue purpose. like, letting two characters get to know each other, humour, comfort, etc.

(this ones short, sorry bout that) comment suggestions and thank you for those voting. I love you guys.