Living that way is tough - have been there off an on. The most important thing is always the rent/house payment. Sometimes you can get assistance with food from a food bank, even if you can't qualify for Federal food assistance. Use that resource as it can free up money for utilities which are of course also important. If you live near where you work or in an urban area, giving up a car to not have that payment can be a big relief, or drive a used car that is paid for and in decent condition. Living in a more rural area, we did not have that option. There are usually organizations that can help with utilities also - ask your utility companies. Sometimes they can do assistance based on your annual income and reduce your fees.
The first things to give up are expensive cell phone plans and get a basic one. Cable can also go - Netflix/Roku save us tons of money and there is programming for the kids. Cut extra stuff that isnt' necessary and always focus on the basic necessities first.