Discounted rail tickets: Up to 80% discount is available. Each rail company has a different name and usually a wide choice of cheaper tickets depending on: how far in advance you purchase the train ticket, conditions of travel and refund options. Go for the very cheapest ticket shown (usually Advance single Tickets - which have ADV written next to them) as available which you are happy with the ticket and travel requirements. Cheap One Way and Return Advance Tickets.
Reservations: Where possible always select for a reserved seat; there is no extra cost. If you can not purchase a reserved seat, you will still be able to travel on the selected train, but you will have to look for a seat which is not allocated to somebody. A seat may be allocated only for a section of the journey and you will have to give it up when the reserved seat ticket holder arrives. Occasionally if a train is very full you may have to stand or lean against something for part of your journey. Book early and reserve to try and avoid this. The earlier you book the better train fair prices you get.