Budgeting tips when income drops - what worked for you?

I am $550 short each month and trying to find it. I have read a lot of threads here and could not find my exact situation. The rent is fixed and the car payment is high. What helped you?

A paper list of bills by due date helped me more than an app. I could see the month at a glance.

Sell things you do not use. I made about $550 from a weekend of listing.