It is important to understand that the search engine spiders need something to read. So the first most important tip is that you must make sure that both the Spider and visitors can find much relevant information on your site. This sounds obvious but the more fresh and informative articles are on one side. The higher the position of an website lies in the SERP the more you will need to update your pages every time to stay on that place.
Always use the Keyword in Title : Remember that the key words must appear in the title. The title of your article whatever you make. Because the users primarily read the headlines first and then enter the content. The best example I can give you is of a newspaper. You have paper in your hand and from number of news you will only choose by looking and reading the headline, not the entire content. This saves your time. The same logic works here for both, bots and users. Many search engines highly weights the title of a page. This is because it is actually a summary of the contents.
Therefore with an view of SEO this point is extremely important. In turn this will also help you to track the position of your keywords. For example you can search the same in Alexa. Put your domain name and it will provide you information on which keywords you are gaining traffic. So it is better to position the keyword in proper place.
Density of Keywords : This does not means that just keep on repeating the keywords in your entire content. It is an kind of ration that you must maintain in your article. Like you must use around 4% in a small content to get it on a better possible. It must stay between 2 to 6%. A high keyword density will simply confuse the bots and that is the place where your site will be affected. This is an kind of trick that are used by webmaster for faster indexing.
Google Adwords : This tool is the one which you can use. It is based on some kind of criteria that you can follow and get recommendations for keywords. Thanks to Google and other PPC services that allow you to test variations of your ad-copy, each other. You also have to find the keywords that generate sales. Again, this is very similar to the search for a good ad-copy, you try your best performing keywords from the previous test ad copy. The biggest change is probably that the features of the Google AdWords Keyword Tool and the Keyword Tool to search queries based on a user interface in combined were.