By definition keywords are words that appear in a text more often than we would expect to occur by chance alone. Keywords are words or phrases used by search engines to help rank your website.
Keywords can be used in three parts of your webpage:
1) The main content of the website
This is self explanatory but you must be careful not to use them too often as this may well result in your site being deemed spam by the search engines and either blocked or ignored. As a general rule keyword density should not exceed 5%. Anywhere between 3% and 5% is good i.e. in a four hundred word article your keywords should not appear more than twenty times. Anything more than that could cause you major problems.
In addition to this filling your text with too many keywords or phrase will not scan well when your visitors try to read it and they will more than likely just leave your website. It is far better to have a well written piece of text that will interest the reader than a piece that is written purely to exploit the search engine crawlers.
2) The title of the webpage
Text placed in the title tag will appear in the title bar of browsers when the web page is viewed. For example if your are selling gardening supplies and the page is dedicated to plant pots the title might look something like this: <title>terracotta pots, plastic plant pots from yoursitename</title>.
The most common mistake made by people when first designing their website is to include the name of their business or domain name in the title tag of every page. This is a waste of valuable keyword space. Don’t make the title of the page too long.
The first three places in the title should be allocated to your keywords avoiding words such as ‘and’, ‘at’ or ‘the’ as these are classed as stop words and the search engine crawler will not read anything after this.
3) Meta tags
These are used solely by the search engines’ crawlers and are not visible to anyone visiting your website. This is what one looks like: <meta name="Keywords" content="terracotta, terracotta pots, plant pots, plastic plant pots">.
Meta tags are used for a lot of additional things by the crawlers other than keywords but that is not what this article is about.