The article below appears on WikiHow. The tips are from American writers but most of them apply to Britain too.
1) Analyze your expenses. Budget your money. Find out where it's coming from and, more importantly, where it's going. This can be a very surprising and enlightening exercise for many people.
2) Find where you spend the most money on a monthly basis. The top two or three items are where you need to do the most work. Read more about How to live cheaply - some American ideas