Pretty straight forward and simple man. Common Sense.
what you make in a month - how much ALL your necessary bills are = how much you have left over for beer and hookers.
But in the interest of being less of a penis:
Over pay a couple months by 25-75 dollars and let it extend your due date. Then once you extend your due date a week or two or four, start having them apply the overpayment to principle. (There should be an option on the pay stub, or the webpage if you pay online.) You should always overpay as much as possible.
This does two things, extends your due date. This will come in handy if you forget to pay your bills, or if you are in a pinch for cash. DO NOT abuse this. Pay on time as much as possible and use the cushion as emergency only.
The second thing it accomplishes is reduces your principle balance faster, which in turn saves you money you would otherwise owe in interest.
If the interest rate on your loans is lower than the interest rate you will earn by keeping your money in a CD or investing it otherwise. DO NOT OVERPAY YOUR LOAN. INVEST IT AT THE HIGHER RATE. A lot of people fuck this up all the time. The point of using other people's money (taking a loan) is to make more than you owe in interest, and then the loan becomes free money.