Any attempt to manipulate natural Search Engine (SE) results listings is frowned upon by the major SE’s. But that doesn’t mean that all SEO is bad; most of it is just plain common sense. There’s no point having a great site that a search engine crawler cannot “see”.
Step forward Google, and their “Search Engine Optimization Starter Guide”. For anyone who’s new to SEO, this is essential reading. And, for anyone who’s highly experienced, I’ll happily challenge that there’s something in here that you haven’t paid attention to in recent months!