In missions where you have to kill an important figure in a certain way (such as pushing them off a roof or into a furnace), you can do this easier by luring the enemy over to the hazard you must use to kill them before fighting with them. Just avoid them and run over to the hazard. They will come over to you. Beat them up a little, but do not kill them completely. Then, grab them and swing them so they have their back to the hazard. Then, shove them to their death.