I got lucky to an extent, i'd noticed that it was continually using location services but closing all apps and rebooting wasnt sorting it. I did check location services as well but there were a few showing as having used it recently. Then whilst i was using the phone it popped up a box saying The Weather Channel was doing something with location services and did i want to change it. I knew i'd not opened it other than just after i'd installed it a few days prior so i changed them to only whilst in the app but then deleted it and i've been fine since.
Unless you get a bit lucky like that its going to be a process of elimination to try and figure out whats causing it. Try checking things like the location services for apps with the purple arrow next to them which are apps thats used location recently and the battery screen to see if it gives any clue as to what has used a lot of battery recently.