Well the basic way of making jam is cooking the material (eggplants in your case) with an equal amount (by weight) of sugar, after that's done soak it with water and let it reduce.
Now that's just the basic, I personally have a special and SECRET recipe for each kind of jam.
Tips:
Spices go really well with sweetness.
Choose the smart way of processing the material.
Experiment with "stuff", it can't hurt.