So for context/to call out my own bias: I had a... suboptimal internship experience early on in my career, so my advice is largely through the lens of not repeating my mistakes.
1. Build a network. And I don't mean artificially; find people who share your interest, who you chemistry well with, who you can help, who are eager to help you. Make friends! (Even/especially if you normally might not do so). I failed at doing this effectively, but even so, my SLIGHT bit of network continued to pay dividends for many years in opening doors + providing friends I cherish to this day.
2. Figure out how you can be helpful to your boss/team/company. Whatever the hell that is (but hopefully in line with what they expect out of your role :) ). Find out what their pain is, where they could most use an extra set of hands with your skill set (or a skill set you can take on and learn!) and apply yourself to making the situation as improved as you possibly can; audit and communicate your success as you go. (Make sure from your mentors/team/higher-ups you're in a good path, you're helping, and are visible; this requires building a good rapport, see part 1)
3. Learn how "the game" is played. Companies, especially larger companies as typically offer internships, are worlds onto themselves. You will learn massive amounts about people, politics, society, incentives, and "economics" (in a very loose sense) if you keep an open ear over the course of a career. An internship is your first chance to do so. Questions like: What is REALLY driving everyone in the team/where does power really lie? How do individuals find success, and how can you replicate this? What do various levels of the company value, and how does this pan out to strategy and reality.
In fewer words/to summarize: Improve yourself, socially and technically, while making a positive impression as a professional asset to the company, and gaining a better understanding of how you'll need to continue to do this over your career.
I hope this was even slightly useful, don't hesitate to ask for clarity or detail if needed.