How to get cheap ticket

There is so much to see and do here in London that it is a waste to keep ourselves to only learning in the classroom. One way that I like to experience London culture is going to the theatre.
There are many good shows in different theatres around London and different ways to get cheap tickets. We students can get a student discount, or you can buy cheap tickets through discount ticket stands around the west end or on some websites like

http://www.discounttheatre.com/

http://www.lastminute.com/