With Necropolis it helps to know Gary and the world Gary grew up in. For most of you the time would be an alien world. Segregated society, a universal draft, and no computers. Story telling was very different, especially in the magazine world. Naive by our standards, with much of the world as great a mystery to the typical American of the period as the extra-Solar worlds are to us today.
It also helps to know what sort of games Gary ran in the early days of D&D®. The kind of events where the players would cut open gator bellies to see what they held.
To get a feel for the kind of adventure Necropolis is, look for old action-adventure flicks on the tube or at the local video store. Especially keep your eye out for compilations of old movie serials. As a matter of fact, if your cable system carries Starz' Western Channel (305 on Cox Digital Cable in San Diego), you can catch tons of old western on it.
Most importantly, you must play your best in Necropolis. Think, cooperate, use your initiative. Be inventive, be creative, be on your toes. Above all remember, in Necropolis the GM is out to get you.