if you can, you'll also want to use Photoshop to make the map rather than Microsoft Paint (for example) because Photoshop is alot more forgiving of mistakes that you make, as well as allowing you to make layers on top of and separate from the actual map, so you aren't permanently covering up whatever you put some color on top of.
you'll also want to have one of our color schemes on hand. depending on what you're going for, use the Universal Color Scheme (UCS) or the Revised Color Scheme (RCS). those cover the most basic countries. there's also TACOS, my own color scheme project, which has alot more options. you can find all of these color schemes via
this page