Roses are really a good helper. You can buy fresh flowers or freeze roses in a bottle, which is also very beautiful. Another kind is a cartoon bouquet with many cute little animals on it. It is cute and beautiful, can be stored for a long time and is not so expensive.
I think it is essential to send a love letter first, the handwritten one. Of course, you can also fold a lot of paper cranes and write a sentence on the wings of each paper crane. Each one should have different words. You can write some feelings from the first meeting her to slowly liking her. Girls will be very moved.
On her birthday, hold a birthday party for her, give her a big bear, put a note in the bear's hand, write "Be my girlfriend, I will treat you well", and some words like this. Make sure the note in the bear is not lost, and remind her to read it when you give it to her.