Taking out graduate student loans on top of undergraduate student loans can be risky. Therefore, it is important to exercise responsible borrowing. Before you borrow make sure you know what your goals are and have a solid plan about what you are going to be doing in life after graduation.
If you have made the decision to go to grad school you probably know what job field you will end up in. As a potential borrower it is best to look at the median annual salary of the job you hope to have and borrow no more than that. With a ten year repayment plan you will be looking at putting 10% of your income towards paying off your loans every year.