Hello all! I was helping a fellow user on HUKD when I had an idea to share all the methods I am aware of to save money on train tickets. There's regularly questions about train tickets, and since I travel by train regularly, but never pay full price because I am really money savvy when it comes to travel, I thought I would create this thread to hopefully help you out!
Links and more info/updates for all of the below will be in comment #1.
Railcards save you 33% on train tickets, and you can sometimes get discount on buying railcards (RRP is £30). You can also use Tesco Clubcard Points to purchase Railcards to save even more. Remember that you MUST travel with your railcard (I suggest keeping it in your wallet/purse).
2. Split Tickets
On most journeys, it is may be possible to split your ticket to save money. For example, a single from A to B may cost £50, but a single from A to C (a calling point en-route to B) may be £10 and a single from C to B may be £15 meaning the total journey costs £25. Remember that the train MUST stop at the station you split the ticket at.
3. Advance Tickets
Sometimes, it is cheaper to buy 2 singles instead of a return, or to book an Advance ticket rather than buy on the day. On most TOC's search engine, you can usually search for all routes for a specific journey (which shows slower routes). This sometimes brings up cheaper tickets, as well as a wider variety of advance tickets available.
Most Advance tickets go on sale 12 weeks before the date of travel, though some TOC's are 24 weeks.
Some websites charge a fee, though TOC's are not allowed to do this. It's best to weigh up the pros and cons of booking from a particular site.
4. Special Offers
Sometimes, TOC's and official ticket sellers (like TheTrainLine and RedSpottedHanky) run promotional offers, and it is always worth looking for these when booking train tickets as they may allow you to save more money. Try and see which promotional offer will save you the most money.
5. Bonus Offers
Some TOC's (like GWR) allow you to earn Nectar Points or other benefits. I find that I earn A LOT of Nectar Points from booking all of my tickets through GWR. Remember that you can book all UK train tickets from any TOC's website, so consider the benefits of booking from each website. Nectar Double-Up is approaching soon as well :)
Virgin Red - 20-30% off West and East Coast Virgin trains services.
6. Tesco Clubcard
As far as I am aware, you can spend Tesco Clubcard points at RedSpottedHanky (£10 = £20) as well as on Railcards, so if you have points burning a hole in your account, then perhaps consider spending them on your train tickets to save even more.
7. Rail Travel Vouchers
Whenever you travel by train and your service is delayed by 30 minutes or more, you are entitled to claim compensation in the form of a cheque or Rail Travel Vouchers. You can then use these to buy train tickets and save even more (or cash the cheque in, effectively saving money on your ticket).
8. The TrainLine Ticket Alert
The TrainLine offer a Ticket Alert service, so if you know the dates you intent to travel, you can enter your email address and the travel information for The TrainLine to then tell you when the cheapest tickets are "on the market".
9. London Underground
The cheapest way to get around on the tube is with an Oyster Card or with a Contactless bank card (both are the same price*).
*You can add Railcard discounts to an Oyster Card, so if you have a Railcard, it's cheaper to get an Oyster Card than use contactless.
Megatrain (owned by Stagecoach) do sell train tickets for some routes, though these are usually select off-peak services, and not every day.
Feel free to add your own methods/suggestions on saving money when buying train tickets...I'll add them to the OP! :D