One of the things to stop doing is going out to pick up odd bits - you will be spending a disproportionate amount by doing this.
Martin Lews has a great table on moneysaving expert.com about dropping down a level - e.g. if you're buying Tesco Finest, drop down to standard Tesco. On average, regardless of which supermarket you shop at, you will save around 30% by doing this.
I'll see if I can find the link.
And be aware that economy own label products are often better quality than those supposedly 'higher'. They tend to use simple, straightforward - so cheaper - ingredients. I have occasionally bought myself one of their Basics ready meals for my lunch - intrigued by the fact that they were only 75p! Reading the ingredients is a real revelation. I had assumed that they would be full of horrible things, but not at all.
Some of their prices are unbelievably low. As an example, a box of 30 Sainsbury's Basics dishwasher tablets costs £1.78. They are just as good as the expensive Fairy ones I used to buy. I now buy dishwasher salt and rinse aid separately, but it's still way cheaper. (A friend of mine works for one of the soap manufacturers, and she told me it's the dishwasher that does most of the work anyway!)