Scared of a budget? Throw some numbers on the page, and then track how much you really spend over the course of the next week and month.
Then revisit your original budget. How do they compare?
It gives you an idea of what is realistic and what is not.
Some things are easy to predict (rent, utilities, insurance) and others may not be (food, gas, clothes, doctor visits). Just focus on the easy things at first, and then remember you can revise your budget as you need to.
Check out Dave Ramsey's budgeting forms here.