On-page optimization (website optimization) can be divided into two branches; factors that depend to the structure of website and factors that depend to content you write.
Website Structure Factors:
Domain: Before you pick a domain name you should know your target audience, and what you intend to sell to them. Try to use major keywords in your domain. Using a .com version of a URL is better than other versions.
Contact page: Design a contact page and put your E-mail and mail address with phone number.
FAQ: design a Frequently Asked Question page. I think each website needs a FAQ page, but it depends to you.
About Us: It is necessary everyone visits your website knows who are you, so design an About Us page.
Robots.txt file: With robots.txt file you can limit access of search engines to your website.
Site map page: Whit site map visitor and search engine can browse your pages easily.
404 error page: Create a 404 error page.
Content Optimization Factors: (optimization factors for every page)
Page Title: use your keywords on page title.
Use h1 header tags: put your topic in h1 header tag.
Keywords Meta Tags
Description Meta tag Keywords
Add image tags: use Alternative Image Text.
Use h2 header tags for sub heading.
Keyword Density: The percentage of times a keyword appears on your page, compared to the total number of words on the page.