Seo relies greatly on keyword optimization. You have to bear in mind three important aspects of using the keywords. These are namely, keyword density, keyword variation and keyword prominence.
Keyword density means how many times the keyword phrase occurs on the webpage. Do not use it so frequently that it looks like keyword stuffing. The search engines would think you as a spammer. However, too little use of the keyword would not catch the attention of the search engine towards your site as a relevant one.
Keyword variation involves using variation of the keyword phrase in your content. You can achieve this by creating plurals, misspellings or changing the order of words in the phrase.
You can attain keyword prominence by placing the keyword in the title or Meta tag and at/near the beginning of the webpage. This will ensure that the keyword is prominent on the respective page and is easily visible by the search engines.
Remember to blend the keywords well into your webpage content.