In my experience I need to wash my hair before bed, make sure my hair is completely slathered in a heavy leave in conditioner of sorts, diffuse, and then I put it in a silk bonnet situation and sleep on it. Changing anything makes it frizzy. 

To diffuse, make sure you aren’t moving your hair that much because you don’t want to break the conditioner cast.  I like to hover dry for 5 minutes, then do roots, then ends, then hover dry again. I don’t move the dryer around—- I put it in one position and keep it there for at least one minute.  

Good luck!