how can i improve?

thank you for bestowing a higher score on tetris upon me

we should have a jstris tournament

ummm

The first thing you should practice is to stack for Tetris clears, removing 4 lines at once with the long piece, as this gives you the highest point scores. You can learn about various techniques and tricks for how to stack better, among other things, on the tetris wiki: https://tetris.wiki/Category:Guides

Another general tip is to use both buttons to rotate left and right depending on which is fastest. Avoid having to rotate a piece more than twice.

For Game Boy Tetris specifically you want to have the "hole" on the left side of the well, because when you rotate the I, S and Z pieces so they are standing up they end up slightly to the left. This means that if your hole is on the left side they don't have to move as far to reach it. Most Tetris games behave the opposite of this, and thus benefit from having the hole on the right instead. You can see an example of the Game Boy rotation here: https://tetris.wiki/Nintendo_Rotation_System

Another quirk of the Game Boy version is that you can influence the randomizer somewhat. If you move a piece back and forth before placing it, an identical piece tends to spawn shortly after. So say you get an I piece you can cause another one to spawn by moving it back and forth a bunch before placing it. This is not so useful at higher speeds but can come in handy in the early game.