With so many options of what may be displayed on a website, it is helpful to know what exactly users are looking for. Where to place your keywords is going to depend on the market that you are targeting and the search engine that will be ranking your pages.
In order to do this, it is necessary to use some of the research tools available to website developers. Some of the best tools in this category include Overture’s Search Term Suggestions Tool ,Wordtracker.com, and Google Sets.

Overture’s Search Term Suggestions Tool does exactly what it claims. A user types in a generic keyword or phrase, and the tool will suggest similar phrases and give a figure of how many times that phrase has been clicked on in a search in the past month.

Wordtracker.com offers users the ability to search for a given term (preferably a generic one), and “dig” further to see how many people are searching for the variations of that term. This tool will also suggest other terms to dig further for, and give the user statistics on how many people are searching for that term.

One very important rule to remember is never use keywords repetitively for no apparent reason at all. For instance, if your phrase is "keyword planning" do not pick a place on your page and say:

keyword planning, keyword planning, keyword planning.... over and over again.
This is a spam technique and will get recognized.

Spam can penalize and even ban your site from major search engines completely.