So far I learned:
-Create icons by pixels not by vectors. When creating each individual icon with pixels, you can get the most crisp and clear when working with pixels versus creating it with vector and resizing it. Vectors will blur out the crisp lines when sizing it down to a small size.
-8x8, 16x16, 32x32, 48x48, 128x128, 256x256, 512x512.
-Use consistent lighting and perspectives.
-Use icon builder or favikon
Here are some good references: