SEO and Developers, welcome. Wow! I can see your hands are dirty with Google Keyword Tool as described in part 1.
So, lets be on and get to the point. Below are the On-page SEO techniques:

:When SE crawlers travels your site, it first seestag.  Tip: So, make it unique for each different page and do not exceed 70 charaters. Trap: Do not include this in header.html if you are making use of master-page or common-code concepts.

Meta tags: Two meta keyword are important for SEO viz. Description and Keyword. 
Tip: In description meta, write about page contains and in keyword write keywords.
Trap: Write no more than 155 characters.

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When you were a student, you used headings to point out important things.
Tip: Use headings tags to encapsulate important things.
Trap: Do not use headings tag for making text to look big.

: In body tag make use of keywords.
Tip: Keep 5-20% keyword density.
Trap: Do not overuse keywords.

: Images looks great to users but are headache for Search Engines.
Tip: Put some keywords in alt attribute of image to describe the image.
Trap: Its a bad practice to make image for texts.

: Link to navigate on site and text of anchor text should be well descriptive.
Tip: Link to some high ranking reputed sites.
Trap: There should be no broken link.

Page size: No more than 100K.
Tip: Make smart use of CSS to replace images.
Trap: Compress images using tools like RIOT, and do not change height and width of image in html code.

Page URL: Smart SEO put some keywords in URL.
Tip: Do not crush the meaning of page to put keyword in URL.
Trap: Any page on site should not be more than 5 directory deep to ROOT.

Validate Your Code: Yes its the most important.
Tip: Use W3C Validator.
Trap: Non- closed tags are seen as shit by search engines. So, be careful.

Emphasizing keywords: Keywords should be emphasized using , where-ever possible.
Tip: Use these tags to make texts more human readable.
Trap: Do not overuse these tags.

So, above the on-page SEO techniques must be taken into consideration by developers to help SEO. As On-page SEO is only 20% of the SEO game, stay tuned to read On-site techniques.