Small Business SEM has a great post on how to use keywords after you have spent a significant time researching for the right ones.

Place it in the following locations (in order of importance):

1. Page title
2. In one or more text links to that page. For example, singapore hotels
3. In the URL of the page like http://www.yourdomain.com/singapore-hotels.html but don’t use more than 2 dashes.
4. In the header tag of the page like h1=Singapore Hotels
5. In the page text like “The following Singapore hotels are the best…”
6. In the META description tag like META name=”description” content=”Singapore hotels that are rated the best by our users are listed below”

Also ensure also the following:

1. Make sure that page titles and meta tags are unique.
2. Also ensure that anchor text is also fairly unique. Don’t stuff the keyword into every link.
3. Write the header tags and page text naturally without stuffing the keywords just for the sake of optimisation

Read the full article here