2) If you are targeting a specific set of keywords, try to repeat those words a few times on the page.  This concept is called "keyword density."  For instance, if you are writing an article on how to cook shrimps, use the words "cook" and "shrimp" in the URL of the page on which the article appears, use those words in the title, and use those words a few times in the body of the article itself. 

That being said, try to maintain a balance between SEO techniques and keeping your website reader-friendly.

3) Use variations of the same word.  For instance, if you want to optimize the word "dance," you might also want to optimize the words: dancing and dancer.  Why?  Because you want to capture all the possibilities in terms of the keywords people will use to find the information you are providing on your site.  The wider you cast your net, the more traffic you will receive.

4) Optimize your use of titles/ headings by incorporating relevant keywords.

5) Use meta tags and meta descriptions for each of the pages of your website.

Notwithstanding the above, the most important on-page SEO technique is to put relevant content so that visitors who come to your site don’t feel they have wasted their time. Some of those visitors are bound to be webmasters and, if they like what they read, might link back to you. This brings us to the issue of off-page search engine optimization.  

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You should never have to choose between the two.  They should go hand in hand.  Should you be forced to choose between the two, you should choose building great content.  Why?  Keep things in perspective.  Search engine optimization is only a means to an end, meaning that it's only one way to drive traffic to your site.  What's the point of getting traffic when the first thing people do when they land on your site is to leave?  You want them to stay.  More, you want them to come back.

The last thing you want to do is to create spam.  A bad site is nothing more than spam.  As search engines become more sophisticated, spam is bound to disappear.  The Web is constantly growing and, as it grows, the competition will become tougher.  The only way to survive online and to get noticed is to have something intrinsically good. 

Great content has another advantage.  It will help build your authority online and help you obtain incoming links.  People that link to your site do you a favor.  They give you a vote.  From experience, good sites will not link to bad sites.  Good webmasters despise spam and will certainly not encourage it.  Furthermore, a good site will attract credible advertisers, those with deep pockets.  Credible businesses sure don't want to be associated with something that will negatively impact their image.

How should you approach building content online?  Don't worry about SEO initially.  Just think in terms of your audience and try to give them value for their time.  Once you've built your content, come back on it and see if you can perform SEO (if you can change few words here and there to optimize the use of some keywords).