1. Arrive early and stay late
Being on time is a given but, to show how serious you are about the internship get there early and stay a little later. Doing this just helps to show your interest in the company and what you are doing for the company.
2. Share your ideas
If you have an idea don't be afraid to tell someone. You don't want to be the intern who doesn't speak up or regret not contributing enough! And never let the size of a company hold you back; a company hires interns for free/less expensive help, however, you bring fresh ideas to the company being young and new to the job.
3. Take initiative
Never wait to be told what to do! Just start working! Make a list of everything you want to do to help or what you think needs to happen. Show your mentor first or just start on your list. Whether you take the time to write down your ideas or actually start on an idea, it is showing initiative because no one had to tell you what to do!
Let me know if you currently have an internship in the comments below!