Regular passengers can make substantial savings by taking advantage of season tickets, which are available part-time (for use on three specified weekdays plus weekends) as well as full-time (for use every day including weekends). Season tickets are available for one week, one month or any period up to a year. Look up prices with the National Rail Enquiries season ticket calculator.
You will need a passport sized photograph for a Photocard when you first purchase a season ticket. You can buy a season ticket from any staffed station.
If you travel often but not every day, another option is a carnet. At staffed stations you can buy 10 peak time return tickets for the price of 9 for certain routes.
There is also a dedicated carnet scheme on the Tamar Valley Line. Read this poster to find out more.