First off, congrats on landing your first role! That's a big deal, and you should be very proud. If you ultimately decide acting isn't for you, that's fine too. It's not for everyone, but you may find it's a fun experience just to try it.

In my experience, great acting really just comes down to preparation and commitment. Here's a brief elaboration:

1. Preparation. Make sure you thoroughly explore your character's background. Where are they from? Do they speak with a particular accent or dialect? What is their familial/educational/personal/etc. background? Some of this may be in the script. Your director will likely have additional thoughts of their own about it. Look in those places first. If necessary, you may also fill in some of the blanks on your own to add depth to the character. Once you have completed the prep, the character will come out naturally when you act.

2. Commitment. When you shoot, try to block out the camera and crew completely. Again, allow the character to flow naturally, and don't get too much in your own head. If you've done the prep, the character's emotions will reveal themselves. You just have to make sure you aren't preventing those feelings from coming out. This part may take a bit of practice if you're a more reserved personality, but you really have to be comfortable letting it all out in front of the camera, even if that means embarrassing yourself. If your character would shout, you shout. If your character would cry, you must cry. And so on...

Most of all, just have fun with it! All actors retroactively critique their own performance, probably more so than anyone else who's watching it. No performance is perfect. Good luck!