Raised £1k from selling old stuff on ebay (clothes, books, DVDs, toys etc).
Raised a similar amount from bigger items at a car boot sale (bikes, tent, etc_ and local advertising such as Facebook marketplace. (car top box, car cycle carrier, old skis, staircase ladders we used once for decorating and won't need again, old garden shed, etc)
Started using supermarket websites to compare prices and buying things when whichever supermarket had offers on. (Rotation of 4 different supermarkets for click n collect or delivery each month). Mostly for packets, tins, and other non perishables which I could buy when on offer rather than when needed and build up a small stock.
Never buy anything when I first see it, whether in the shops or online. Sleep on it and go back the next day if I still want/need it. 90% of the time I forget it so clearly didn't need it!
Use comparison websites for everything, car insurance, house insurance, utilities, phone, broadband, etc,
Review direct debits and standing orders every 3 months to check I'm not paying for something i don't need/use anymore.
Look at petrol station prices as I drive past various filling stations and fill up when one is far cheaper than the others.