Use a good heat protectant spray before styling your hair with any heat. eg. straightener/ hair dryer. Leave in conditioners in conjunction is a good idea too. Also doing a hair treatment once a week really helps too. I personally love Redkens all soft heavy cream. This stuff is amazing.
Try and limit straightening your hair to only once or twice a week. If you have a good straightener it will stay straightened for days. I also have fine hair, another good tip to keep it silky and straight whilst you sleep is to use a satin pillow slip or if you don't have one of those, slip a silky cami over your pillow.