Oak tree sap is one of the better ones to deal with - just wash your car! The stuff I'm talking about is just the tiny little drops that appear as just little clear specks - like it is just starting to mist on a dreary cloudy day.
Warm water works well on sap. When all else fails you can try claying.
Sap is a PITA. Now we're into pollen season and along with it comes the sap. Plus, it's windy most days. So for 5 minutes after washing the car or dusting off the car it's clean and then a gust of wind blows and it's like I never washed it.