Protips:
1. Draw in at least 128x128 resolution, then shrink the image to 64x64 and add a sharpen filter (the only good filter).
2. As I can see in this pic you made, I recommend you to stay away from MS Paint (if you aren't using MS Paint, then stay away from tools that lets you draw pixeled lines) when it comes drawing wc3 icons. Pixel art will awfully clash with icons made with non-pixel art icons.
Use either Photoshop, Paintshop Pro or GIMP and experiment with the available 2D art tutorials (both in Hiveworkshop, Wc3Campaigns and Google) so you can improve with shading, definition and color blending