For a week write down everything you buy, down to the 10p you put in the charity box. Get your OH to do the same. Then work out all your bills.
With your bills see if there is anything you can cut back on, we rang sky and told them we could not afford it and they gave us £20 a month off. Is there a cheaper tarrif for your gas and electricity.
With your day to day spends get two different coloured highlighters. Colour all your essential spends in one colour and none essential in the other. Do the same with your supermarket bill. Did you really need that multipack of crisps and two bottles of wine?