What's the best way to show my girl that I love her?

Take her somewhere special and tell her. Write her a letter telling her, give her flowers and call just to say you care. You could get her a promise ring and tell her then too. all these things are sweet and will let her know eathier way you do it just be sure to tell her with your own words as well! she will be sure when she hears it from you!

You have to prove to her the best way you know how, that you care for her as much as you say you do.

It all depends on the girl really. For me, sincerely listening to me when I talk shows care. Many men have an issue with being attentive. Attentiveness conveys genuine interest (but not too much, you don't want to end up being considered a stalker)...Also, find out the things she likes to do and do them with her. If she has her eye on a gift or trinket (and you can afford it) give it to her "just because". some women like flowers and candy (never have, never will)...some women just want to hold hands and cuddle. The trick is I guess, finding out what she likes, and doing those things...

Okay, we're going to get creative... get a poster board, some glue, and markers and flowers. Press the flowers so they're flat. Like in a book, google it? Anyway, when the flowers are flat, glue them to the poster board, and write something sweet on it, and include some pictures of you two together on it. Make it kind of like a collage of stuff that is important to her, or both of you, but make it mostly about her. This is easy with some time and imagination, and it'll really show her that you care if you make something for her. How many other guys had taken the time to do this for her? Not many I bet, and it will be a great surprise.