This is one of the most important things that you will have to do for every website that you will create in your life. First, you will have to decide what the keywords are that most people may use when they want to look for what you are providing. Think about the words people would use to find your site, and the more people who contribute, the more exhaustive the list is going to be. After you have narrowed down the general keywords that you think that people will be looking for, you can use specific software like Google’s keyword tool, Yahoo’s Overture Keyword selector tool, Wordtracker, Keyword Dictionary or any other tool that you are comfortable with.
Most of them are free to use and will give you a combination of keywords based on the keyword that you typed in. This will help you identify the best combination of keywords to use in your content because it will give you the search strings that are the most commonly used in relation to the word you typed in.
Be dynamic, not static
This does not mean that once you write and post your articles you are finished. Keywords are very dynamic, and often, along with trends the search strings that are often used too often will change. You do not have to necessarily change the entire content in your site during times like this. Just making sure that you incorporate the new keywords is sometimes good enough.
Don’t overdo it
This may sound simple but in reality it is not. This is because you will have to walk a fine line between over-stuffing your articles with different keywords and with putting in too few. And even then most search engines are able to identify if the keywords come logically as part of the sentence or have been forced in somewhere where they are not suitable.
Nobody knows exactly how the search engines do this as it is their trade secret, but suffice it to say that just because your article is full of keywords it does not necessarily mean that the site is going to get a better ranking. Often an article with the keyword appearing just once will pop up higher than one where it has been repeated a number of times. Keep this in mind when writing your articles.
Also never copy content, unless you are linking back to where you are copying from. All search engines are able to identify copied content and if it finds that your article is copied, you will even lose ranking because it will tend to push your site to the bottom of the pile.