Start with the keyword research with the help of google keyword planner and after that prepare the meta data and other content with the help of those keywords.
There are couple of things that are probably the most important when it comes to on page optimization.
xml sitemap
meta tags
These are the two most important things in on page optimization so you should always work on these in order to get good results from your on page SEO work.
Try reading Google’s own ebook on Search engine optimization. I’ve gone through through myself and it surely does teaches you and helps you a lot if you’re looking for page optimization.
There are lots of tools are available like title and description optimization tool, Microsoft free SEO tool kit, You tube keyword tool, keyword eye basic, Robots : text generator and many other tools are available which helps you in on page optimization.
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.