Are you thinking about adding a print button below your blog post? There is a great plugin for this. WP-Print.

If you are a genesis user, there is another great one. Genesis Printstyle Plus.

We like to add print style without using any plugin.

The code below is to be added into your genesis theme style.css

/* # Print Styles
----------------------------------- */

@media print {

	.site-header,
	.nav-primary,
	.breadcrumb,
	.entry-meta,
	.site-footer,
	.entry-comments,
	.comment-respond
	{
		display: none !important;
	}
}

The above code works flawlessly for a one column layout theme. If you have 2 or 3 column layout theme, you need to add .sidebar, .sidebar-alt to the above code. If you want to add further element you should inspect through Mozilla Firefox->Developer->Inspector.