I usually try to match the tuning of the directly opposite tensors, listening to them from the same distance. What really bothers you when it comes to adjusting your skin is the sound of the other parts of the skin. Once this is done, it is about matching these diameters between them.
Be careful about using Vaseline in warmer climates as it can melt and break down. White lithium grease is a good alternative. A good tuning reference is a Dm7 chord - D-F-A-C. Though there are other ways as you said.
