Tell them in advance how many hours you will need to do, and be sure that this is ok with them. Explain that they will need to fill out a detailed evaluation of your performance, and go over it with you after they have filled it out. This only needs to be done once, at the end of the Internship. While many students find themselves absorbed with the process of getting an Internship, their efforts shouldn't stop there. What you get out of an Internship depends, at least in part, on what you put into it.
Internships represent a unique combination of a working experience and a learning experience.
While most learning experiences are abstract in nature, Internships are concrete experiences. And while most workers get a limited amount of support and training, as an Intern you may get more attention and support than you ever will again in your professional career. As an Intern, you may find yourself able to take risks and try creative things that you may not feel comfortable doing as an employee. When volunteers are called for to perform a variety of tasks, raise your hand. Show interest in different jobs and tasks and enthusiasm for learning new material.