Find out the keywords which are searched widely by the people on internet. You can use free Google keyword tool, to see how many people are searching for your keywords every month. Don’t go by the competition bar in the Google keyword tool, as it doesn't give you the actual competition. The Google keyword tool is designed for the advertisers and only tells the competition among the advertisers.
Remember, “Google Keyword Tool is only used to find the number of people searching for a particular keyword.”
Now check how many websites have that keyword in them. You can use search engines to get this data.
Do some research and find the keywords which are searched more and used less in other websites. These are the phrases that drive traffic to your website. Find around 100-150 such keywords and use them in your website. It is highly difficult to manage such huge number of keywords list and I know you must be wondering how to use them on your site. Follow the following simple suggestions given below and all your doubts will burst like a balloon ;-)
Make sure that the top 6-7 keywords with highest weightage out of 100-150 keywords are used on your home page and scattered throughout the website.
Remaining keywords can be confined to specific pages of the website.
For your information:-
The phrases that are scattered throughout the site are called site wide phrases
The phrases that are confined to specific page are called deep phrases.