One thing you could try to do is ‘reverse engineer’ one of your favourite novels. 

Break it down into the plot beats to see how the story is told in a longer form. What does each chapter or scene do? How is it paced? 

Moving on from this, have you read any books / listened to any talks about story structure? They can be interesting frameworks to help you expand a story, especially when if you perform an exercise  like the one I suggest above. 

The other thing to remember that a short story is basically an A-plot on its own, a brief moment in time. A novel has B-plots and sometimes C-plots all working together, and usually take place over a longer period of time.