How can improve a rough diamond?

Answer 1

You can cut the diamond. Cutting it uses a tool sort of like a chisel, that actually breaks the diamond. When you cut a diamond, (if you do it right) it exposes a flat face, or facet as they are called when it's a gem. By cutting it several times, you can make it so that all you can see are the facets you created by cutting it, and it becomes the gem we are all familiar with from jewelry.

Note that this work is only done by professionals using professional, diamond-tipped tools.