Careful which website you use
Rail operators will sometimes offer deals on their own websites, which do not appear on other sites. Third party websites may charge you extra.
Generally speaking, the earlier you can book your ticket the better deals will be available. Tickets go on sale up to 12 weeks before the departure date.
National Rail Enquiries has a handy webpage that tells you the latest date for which you can book tickets with each of the rail operators.
Be advised that Advance tickets tie you to particular trains and times.
If you qualify for a railcard, this is a great way to save money. See if you may be eligible here.
Take your time
The Campaign for Better Transport advises that slower and non-direct trains can be cheaper. It says to "tick 'include slower trains' on the National Rail Enquiries site".
It adds: "Sometimes buying a ticket for each individual leg of your journey can be cheaper than buying one through ticket and you won't have to change trains."
Beat the new year
Most fare rises kick in from January, so if you are able to buy your ticket for the year ahead before this date, you will save money. Passenger Focus points out that fares can also be revised in May and September.
Yourmoney.com advises: "Ask your employer about company schemes or any assistance that they might be able to provide to help spread the costs of an annual ticket. Annual tickets are cheaper than purchasing monthly and some employers offer an interest-free loan to help cover this."
Some rail companies also offer flexible season tickets.
National Rail's season ticket calculator allows you to compare different price options where available.
And make sure you buy before 2nd January when the fare rises come into effect.
One helpful reader of the Campaign for Better Transport website points out that booking clerks at railways ticket offices "will usually happily spend 15 minutes trying to knock off a further few quid for you" if it is a quiet time of day.
Using a ticket machine does not help either.