print.css don’t know how to manage

I followed some instruction that I find in threads and in wp codex to have a better print function of any page or post.
The problem is that I do not understand how to define which part of the page will have to be printed; particularly the navigation area, that it is placed in the middle of the printed page.
this is the code I used

/* Print Style Sheet */
@media print {
.noprint, #noprint { display: block; }
header nav, footer, #secondary { display: none; }
navigation { display: none; }
#primary { width: 100%; }
#body { background:white; color:black; margin:0 }
}

Any suggestion is welcome.