The easiest way to impress your girlfriend is to pay attention to her! If you actually listen to what she is talking about, you will know exactly how to impress her.
You need to mix things up so she will notice you are thinking about her more. If you never send her texts, start sending them to see how her day is going or to say you are thinking of her. Not down with talking on the phone? Suck it up and start calling her more, she will appreciate it. You don’t have to go over board but she will notice even a little effort.
Dress up a little bit more when you go see her. We all get in routines where we just rock some sweat pants and a hoodie when we are going just hang out with our girlfriends. This is fine to do but sometimes you should wear a button down shirt and clean yourself up a bit more when you see her. She’ll ask what the occasion is and respond that you were thinking of how beautiful she is and you wanted to look good for her.
Go out of your way for her. It might be a pain; but rushing home from work to visit her or driving a long distance just to hang out with her for a little bit gets you major points. A lot of guys make their girls put all the work into a relationship. By going a little above your expectations you will be a shoe in to impress her.