My advice to future interns would be to take initiative. Choose to take on projects that seem challenging, especially if they seem interesting to you. For a project to turn out well, it has to show that you care. Don't be afraid to ask your supervisor questions, but if you're confident that you know what to do, don't be afraid to act without reassurance. Also, welcome feedback, even if it's more negative than you want to hear. The best supervisors are critical, and they don't accept less than your best. Ask for and act on their advice, and your work will improve dramatically through the internship.