For best search engine optimization, you must use your keywords and keywords phrases effectively.

For optimal effectiveness, use different keywords and/or keyword phrases on each page of your website. Optimize each page for those keywords and/or keyword phrases that are relevant to the content of that particular page.

Title Tag

-Use keywords and/or keyword phrases as a descriptive title for each page.
-Use your most relevant keywords and/or keyword phrases in your home page title.
-To be the most effective, title tags should contain only keywords and/or keyword phrases.
-Repeat the keywords and/or keyword phrases 2-3 times but make sure that the title makes sense. An example for this page would be: Keyword Usage, Using Keywords and Keyword Phrases Effectively.

Meta Tag Keywords

-Place all relevant keywords and keyword phrases in your meta tag....
-If possible, avoid using single keywords as they may be too competitive. Use keyword phrases instead.
-Don't repeat your keywords more than 2-3 times to avoid offending some search engines.
-Separate keywords and keyword phrases with commas or spaces, not both. Example: keyword,keyword phrase,keyword or keyword keyword phrase keyword.
-Use common misspellings or miss keyings. Ex: keywrod or keywird.
-Use different forms of keywords whenever possible. Ex: web site and website.
-Use singular and plural versions of keywords. Ex: website and websites.
-Use upper and lower case. Ex: Website and website

Meta Tag description

-Use your keywords and keyword phrases in your meta tag description.....
-Repeat your most important keywords and/or keyword phrases a minimum of 2-3 times.
-The total length of your description tag should be no more than 20-25 words.
-Your description should make sense as this is what often shows up in the search engine results page. This is your opportunity to persuade users to click through to your site so be sure your description is enticing and contains keywords and/or keyword phrases that will attract visitors.

Content

-Many search engines concentrate on the first 250 words of your text when looking for keyword relevancy and density so concentrate your keywords and/or keyword phrases there.
-Strive for 5-7% keyword density (5-7 keywords and/or keyword phrases per 100 words of text). If your keyword density is much higher than this, your copy may not make sense AND the search engines may consider it keyword spamming.
-Use your most important keywords and/or keyword phrases throughout your copy but without sounding repetitious.
-Use your most important keywords and/or keyword phrases in your H1 tag. To give more weight to your H1 tag, use only one H1 tag in your copy. (Your H1 tag should contain your most important statement so you shouldn't need to use more than one H1 tag.)
-Use keywords and/or keyword phrases in your image ALT tags. For example your logo ALT tag should say something such as: ALT="keyword logo image".

META tags are not as important as they once were as most search engines are now searching your copy when looking for keywords and/or keyword phrases. Therefore, it's become increasingly important to have the first 250 words of your copy be keyword rich.

Sometimes, it may be better to write your content first, then choose your keywords and/or keyword phrases from the content. Rewrite your content as needed, adding keywords and/or keyword phrases that pertain to the theme of the content. In this way, you've chosen keywords and/or keyword phrases that are relevant to your content, instead of trying to write content to fit your keywords and/or keyword phrases.