There's english signage to designate which platform and train line is departing from.

Not limited to Japan, but the major issue I observe while riding trains around the world is people are usually on the right train line, they're just not going in the right direction.

So for example at Yokohama Station to get to Kawasaki Station or Tokyo Station, follow the signs to the Tokaido Line "for Tokyo" and not "for Atami"

The link on the JR website has a good railmap you can use as well.

I think a harder issue is the larger stations that have multiple entrances/exits, for example Shinjuku Station has a billion, thats where I find the Tokyo Billingual Atlas useful as it lists the station and shows where each exit leads off to.

Stations also list exits and where they lead off to, look for the large Yellow signs which show the exit name and where they lead off to.