Federal loans are all the same rates for everyone. They are now fixed: Stafford at 6.8%, and GradPlus at 8.5%. As long as you don't have horrible credit history, you will qualify.
If you max out these government loans, and have to get private loans, then yes, your credit history will affect your interest rate. Usually private loans are variable, but the margin above the prime rate, or LIBOR, changes based on your credit.
To have good credit, you need to have SOME history. I'm guessing a personal loan that is completely paid off is best. A personal loan that is close to the max amount... not as good. The whole scoring thing is pretty complicated, and not intuitive. Obviously, if you can avoid private loans, do so.