oh what beautiful things I'll wear
Let's see here, you've gotten quite some critique already. I think the main problem here is the lack of a basic idea. In itself, the picture is quite boring: a simple white rabbit next to a clichéd heart-shape in a boring point of view. Even the colours feel bland. Using pixel-art is not an excuse to draw things from the side, nor is drawing with a mouse.
There also seem to be issues with the bunny itself, weird front legs, shading, the weird second ear that doesn't seem to fit it's profile stance.
Before you draw your picture, may I suggest you draw an actual picture first, even if it isn't any good? Just to hand YOURSELF a base of what you are planning. "Is this an interesting image?"