I’m not great at giving pointers, but generally I’d say:
• try to get a basic grasp on human anatomy first.
• draw all proportions a little more rounded, I try to make the chin, hips, arms etc a bit wider and round.
• fat has weight, make sure when drawing fat it hangs down a bit, or pushes against clothes a little tighter.
• experiment, study irl pics of fat people, and practice over and over.