Writing a keyword list for your site is one of the first steps in your SEO campaign. If you engage an SEO consultant the first thing they will normally ask you, before working on your site, is for a list of your keywords. The importance of writing a good keyword list should not be underestimated. Here are some helpful tips to help you create yours;

Terms You Would Use
First write all the search terms that you yourself would use when searching for a site, product or service like yours. Write every term you can think of that might be relevant to your site.

Your Website Logs
Have a look at your website stats program to see what search terms your visitors have been using to find your site. Add these terms to your keyword list.

Internal Searches on your Site
If you have a search box on your site and can record what terms your visitors have been using it to search for, add these terms to your list.

Competitors' Sites
Get ideas from your competitors' sites. Look at their meta keyword tags and the content they use on their website pages, to get an idea of the keywords they have been using.

Ask Others
Show your site and your current list to people you know - whether they be work colleagues, friends, family or members of a forum you participate on - and ask them to suggest terms. You might be pleasantly surprised by how resourceful and helpful others can be.

Synonyms
These are different words that have the same meaning. Go through your list and add as many synonyms as possible. Use a Thesaurus if it would help.

Spaces
There are some words that are commonly spelled, with and without a space. E.g. Marketplace & Market Place, and website and web site. Use both version.

Hyphens
Where applicable, use the hyphenated version and the version without the hyphen. E.g e-commerce and E-Commerce.

Your Business and/or Website Name
Your list of keywords should include these. People will search for your site or business name.

Location Words
Add these to relevant terms. E.g. if your keyword is business forum, use Irish Business Forum and Business Forum Ireland.

Relevant Websites, Blogs, Review Sites and News Media
Have a look to see what terms they are using to describe your product, service, subject topic or business.

Related Terms on Search Engines
Most search engines will prompt you with related terms when you search for one of your keywords. Add these related terms to your keyword list.

Singular and Plural
Most search engines treat the singular and plural version of any given word as separate search terms. Go through your keyword list and add the plural or singular version of all the terms already on it.

Spelling Mistakes
Look through your list with a view to finding terms that have common spelling mistakes. Add the misspellings to your list. Also add UK and US English versions of the spelling, where relevant.

Keyword Tools
These tools suggest additional keywords to you based on the search terms you enter. My favorite is Google's Keyword tool.

Spending a couple of hours on this process should give you a huge list of keywords relevant to your site and your next task will then be to rank these terms in order of importance.