Congratulations on your first day!
Here are a few thoughts that you might find helpful.
Be teachable. Prioritize learning what you didn't know you didn't know.
Don't try to be an expert. I call this the "amateur expert" phenomenon. It's OK to want to be an expert and to strive for that every day. But it takes time. And the only way to get there is to listen and learn.
Be approachable. Don't be too busy for people. Yes, everyone appreciates a good work ethic. But it's more important for people to want to work with you. If you don't make time for other people they won't make time for you.
Don't make it a goal to impress anyone. Your work will speak for itself. Focus on making steady progress every day and you will naturally stand out.
Triple your estimates. No matter what you're asked to do, until you've done it several times it will take you a long longer than you expect. If you have the option to influence how much time you're given to do the work, under commit and over deliver. This is way more important than some people think.
Be nice to others, but not too nice. If you're super nice to people, they'll expect that from you every day. And when you have the inevitable "off day", people will get way more upset with you just because it's such a big contrast. So be nice, clearly. But again, let it flow naturally. Don't try too hard.
Learn how to make mistakes well by placing small bets and learning from your mistakes. You're going to screw up. Sometimes you'll screw up and people will tell you. But if you keep screwing up two things will happen. First, people will stop giving you opportunities and you'll eventually wither and probably either leave on your own or be asked to leave by your boss. Second, people will stop telling you when you screw up. They will lose faith in you. And this is a terrible place to be. Avoid this at all costs by simply learning from your mistakes.
Batch up your questions. As you learn all the ins and outs of a new environment you'll have many, many questions. And no matter how much you learn over time, every time you move to a new environment you'll go through this process again. You'll see things in the code that don't make obvious sense. You'll have ideas about how to improve things. Some things will start to make sense as you just spend more time with them. Other things you will need help with. What you want to do is try to be as efficient with other people's time as you can. If you ask questions constantly it will begin to annoy your co-workers, even if they say it's ok. So write down your questions as they come up. Make an honest effort to figure things out on your own. Then schedule time once a week or so with more senior people. They'll appreciate you making it so easy for them to help you and some of them may even become your champions.
Invest in relationships. As you take on more and more responsibility your ability to influence other people will become more and more important. It won't be enough to simply solve problems. People won't follow you just because you have answers or experience. But when people feel connected to you and know that you care about them as people, they will want you to succeed and go a long way to help.
Continue to learn on your own time. You will have some opportunities to learn on the job. But you will also make a lot of mistakes as you learn. Think of the time you invest outside of the office as study time and what you do in the office as the test. Contributing to an open source project is a great way to try things out and get feedback from people with more experience.
I wish you the best out there. Take care and enjoy the ride :)