I'm a huge Dave Ramsey fan. Here's a link to his budgeting tools:
http://www.daveramsey.com/tools/budget-forms/
He recommends a zero-based budget (will explain in a sec) that is re-done at the end of each month in preparation for the next month. Because December will have different expenses than February.
So you write your income for January 2013 at the top of the page. Then you go through his budget form and write down every single expense you will have, and everything you want to spend money on, until you have spent every penny, on paper, on purpose. Then you follow it without question.
It will take several months to get a sense of what you should budget for groceries, school expenses, etc. But stick with it and you will find it very rewarding. We use cash for everything and when the entertainment envelope is empty, we're done for the month. When the eating-out envelope is empty, we're done.
Google "sinking funds" to learn how to save up for those big one-time / yearly expenses like renewing your car insurance, spending at the holidays, etc. We have a bit taken out of our one paycheck to cover those things - $10/month to save up for Halloween (costumes and candy), $100/month for the holidays, etc. Then the month before those events happen, we take the money out of the bank and spend it! It's so amazing to leave the store and know that no bill will be coming in the mail!
It will take a while to get yourself organized. Give yourself grace and keep plodding through it. I bet by April you're rocking your budget. Hope that helped!