I'm just starting to really nail my budget down, and it has taken time. So my recommendation is to give yourself some time to really get to know your spending habits -- don't be in a rush, or too hard on yourself at first! Here's how I have done it:
I signed up at mint.com and categorized everything. This gave me the chance to look at our spending over the course of a few months very quickly. And being forced to categorize each transaction helped me immediately find things to cut out (like a bunch of "services" related to our credit cards, subscriptions to websites we'd forgotten about, etc). It helped me come to some hard realizations, too (like the fact that we needed to pull DD out of her childcare situation because it was too expensive).
To work on cashflow I use a dry erase calendar and write in our expenses each week so we can tell when big things will hit during which pay periods and (try to) avoid going broke those weeks.
Now I am working on an excel spreadsheet for our budget to guide us through the next 10 months. I may use the website pear budget to help us keep track, or maybe not.
good luck!
