Through SEO you can boost your website visibilty,Get wide reach-focus locally, nationally and even internationally.It is one of the best cost effective promotional tool.
Also there are two types of SEO-White hat and Black hat SEO.
Black Hat search engine optimization is customarily defined as techniques that are used to get higher search rankings in an unethical manner.
White Hat SEO refers to the usage of SEO strategies, techniques and tactics that focus on a human audience opposed to search engines and completely follows search engine rules and policies Or any SEO tactic that maintains the integrity of your website and the SERPs (search engine results pages) is considered a "white-hat" search engine optimization tactic.
White-Hat SEO Tactics:
1. Quality Content
2. Use Structural (Semantic) Mark Up and Separate Content from Presentation
3. Titles and Meta Data
4. Keyword Research and Effective Keyword Use
5. Quality Inbound Links
And last but not the least keep them updating.