Budget 101 for freelancers is to think and remember you are running a business effectively, and always consider the two - personal and business cash flows separate.
Pay yourself a monthly salary that pays all bills plus a little luxury plus allows a small amount to be banked and saved each month, with the end aim of a personal rainy day fund that equals 18 months of that current salary level as a minimum.
For the business - don't turn work down - if need be pass work onto colleagues friends and trusted third parties - always say yes you will help your clients even if not personally doing the work. Retain a healthy amount of cash in the company to weather drier times, unforeseen bills to the company, and potential future growth (where you hire additional resources top help achieve more and bigger projects).