Know the prices of things you have to buy regularly so that you will recognise a genuine offer. If you can afford to, buy toilet rolls, kitchen rolls, shampoos, washing up liquids - everything you will need but won't go off - in bulk when it is on offer.
Never, ever shop when you are hungry, you will spend a lot more on goodies you wouldn't normally buy.
If your inclusive or minutes don't include 0845 or similar numbers always use this site to find a 'proper' phone number.
http://www.saynoto0870.com/
If you regularly use your oven for small amounts of food such as a pie, baked potatoes or one or two chops think about buying a cheap combi microwave. Mine was under £50 from Aldi and is much cheaper to run than the big oven.
Use Invisible Hand so that you can find goods cheaper when browsing online:
http://www.getinvisiblehand.com/
If you buy a magazine regularly a subscription will be cheaper.