Major advancements are being made in providing multi-language support on the subway systems making it much easier to get around. Ticket machines, station names, as well as maps and guides of the subway and the local area are often provided in a number of languages.
In the larger cities such as Tokyo and Osaka, there are often subway stations clustered in similar areas. Changing lines can be expensive, so check the map closely to see which train lines you can access your destination from. For economical travel, research one-day or two-day passes which will almost certainly be on offer. Be aware that as it is the subway, your JR Rail Pass is not valid. However, it is possible to use your Suica Card, as well as a number of other local IC cards when using the subway.
In some of the bigger stations, there are transfer only gates where passengers don't exit the station but move onto a different line. This can be a little confusing so be aware of this when exiting through the ticket gates. If you are unsure about the price of a ticket, simply purchase the cheapest one and adjust the fare when you exit at your destination—there are fare adjustment machines next to the ticket gates.
For ease of travel and peace of mind, research the subway system in the area you will be traveling in. Many of them have sites in English. If you plan to travel exclusively by subway, research the various passes available to ride economically.