Keyword research forms the foundation for your search engine efforts. If done thoroughly and correctly then that's most of the hard work completed. If done through guess work or with little thought then all your optimising and submitting will be in vain.

Crucial to keyword research is to condense the essence of your site/business into two or three worded phrases, and to get these phrases from a variety of sources. Remember, visitors will probably not have the same vocabulary as you. You may sell a 'high density polyethylene tibia protection system' but someone like me is going to search for 'football shin pads'. It's important to understand what your potential customers might type in rather than established expert customers. After all, the main goal of search engine optimisation is to attract 'new' visitors.

Steps to successful keyword research

Begin with your own ideas for words
Look at your site and make note of any phrases used
Look at competitor sites and their source code (View - Source)
Ask customers. (I've actually heard of a company whose helpline operators ask their customers what phrases they used to find the site).
Ask other members of staff
Enter the top 20 or so keyphrases into a few search engines and examine the top 5 sites that appear to see how they are using that phrase and what other phrases they are using which may be relevant to you.
Check out the GoTo suggestion tool as well. When entering into GoTo to get frequency amounts, always check other suggestions that appear as they may be more popular or will open new avenues that you can explore.

Here are the links to both the UK and USA suggestion tools:

UK - http://inventory.uk.goto.com/inventory/Search_Suggestion.jhtml
USA - http://inventory.go2.com/inventory/Search_Suggestion.jhtml

Choose your words carefully

When selecting your keyphrases look for one or two phrases that generally sum up your whole site/business. This phrase should then be used on every page to help confirm the 'theme' of your site.

Then look at getting a few more phrases that describe your products or services in a general way. For example, for DVisions this could be:

UK affiliate programmes
Search engine optimisation
Directory submissions

Then, if appropriate, go for some very specific phrases. These will not generate a lot of traffic but they could bring in some highly targeted leads. If someone is searching for that phrase they probably know exactly what they want.

When choosing keyphrases also take into account how many sites you will be competing against by carrying out searches in the major search engines. One particular phrase could mean you're competing against 100,000 sites, whereas another similar phrase might reduce that figure to 10,000.