Look at the big stuff too, it really really really tedious, timeconsuming, and requires you to talk to utter morons often, but you need to make sure that you have the cheapest possible:
Electricity
Gas
Telephone
Mobile deal
Broadband
If you have any loans, mortgage, see if you can consolidate, reduce rates, reduce payments, move company.
Check out moneysupermarket.com, or similar, he has a good priority list of what to deal with to reduce outgoings.
Shopping, bulk buy at Lidl etc for basics, write a list for other stuff and DO NOT BUY ANYTHING ELSE. Do not go to the supermarket hungry. Make packed lunches for work etc. Picnic in the park now the weathers good, avoid the cafe. See if there are council schemes for activities you do regularly, like a swim card etc.