The metro can be unbelievably crowded during rush hour. The Subway is also a major tourist attraction in itself thanks to the beautiful decorations of the stations.
There are metro schemes only in Russian in every car, sometimes there are schemes at the stations. It might be useful to print out our metro scheme or to buy it somewhere.
When you're on the station and want to find out the direction you need just look up there're signs hanging on the ceiling, signs are in Russian too, if you are unfamiliar with the language, it may make sense to "count the stops" to your destination or keep your ears open, the conductor will let you know what station you are on.