Standards when creating Icons

I'm in the process of creating some icons for an application, and find myself coming up with the same question over and over again. Are there any guidelines for how thick the lines should be in an icon. I need to use lines with strokes that vary in thickness, but I don't know if there is any standard for it. Let's say the outline of my icon is 16pt, should the lines inside be ideally half of that? Is it better to use odd or even numbers? Any other tips or suggestions?