Have you ever sat down with three months bank statements and categorized where its going?
Its a really good starting point.
Start with big headings for example... mortgage, loans/ repayments, childcare, supermarket, heating/ power, council tax, house insurance, car insurance, petrol, cash.
Once you've put the totals into columns have a good look through at any that seem high. You can get averages for power spending for your house size for example.
When I did this many years ago I was horrified (I was married two good incomes no kids) we spent over £600/ month (between us) at the supermarket - I would have guessed about £250! We threw away quite a bit which I was aware of but also got invited out and ate out a lot and also shopped hungry at lunch times because we weren't organised at sorting lunch before we went.
Then you can go onto look at breaking down what you buy at the supermarket - whether you can spread debt, whether you'd be better off paying your insurance upfront rather than spreading it.
Knowing what roughly what each pots budget is each month then helps you to not realise you've emptied the account again. I'm a fan of hard cash spending on a monthly basis to get used to a new budget - you see the money going down but also know what you have to treat yourself.
Just some thoughts, I'm no expert, but have lived to a variety of budgets in my life - currently a very tight one I have to watch carefully but live within.