Namechanged for obvious reasons.
Family of 2 adults, 4 children and 1 cat. Monthly income of £3620 after tax
Outgoings:
Rent: £800 (includes water)
Electic: On a meter, roughly £30 a week but not sure as just top up as and when. Cannot change to DD as landlord put the meter in before we moved here
Diesel: £120 a month roughly. Again don't really keep track as we both top up as and when
Council tax: We don't pay by DD as DP paid it off all in one go when we got the bill. Will be paying by DD next time
Internet: £26 a month
Mobiles: £150 a month for 3 phones
Car insurance: Paid in one go so no DD
Car tax: £18 a month
Debt: £360 a month
Food: No idea. We don't really do a weekly or monthly shop. Just buy day to day depending on what time people will be home/what kids have after school/school lunches/if we are eating out
Cat: About £20 for food, pet insurance
I've just gone through the bank statements and realised we don't have contents insurance 
Debt: Loan of 10k, credit card 2k
Savings: about 13k split between an ISA and a savings account.
I know we could use all the savings to pay off the debt but ideally we would like to keep them for a house deposit.
I know we are terrible with money. Everybody just seems to buy what they fancy without really thinking about it. DP and I have just sat down to budget but where do you start? Realistically I don't know about meal planning or food budgeting, i've always been terrible at it and its easy to just go day by day. Bank statement is full of £20 shops at the co-op or Budgens. Inevitably we end up picking up crap along with each shop which pushes the bill up.
Where do you start? Is it unrealistic to think we could put £500 away in the savings each month?