In regards to your opening question, it would be the course of wisdom to check out Chapter 4 of moz.com "Beginners Guide to SEO."
Chapter 4 discusses in detail the basics of on page optimization and specific technical aspects of building (or modifying) web pages so they are structured for both search engines and human visitors alike.
In general, all 10 Chapters of this "Beginners Guide to SEO." provides an abundance of accurate, detailed, and very useful fundamentals of the many aspects of SEO. But in regards to your question for assistance with regards to on page optimization Chapter 4 will be of great use.