By now, you should have already chosen a niche. Now, you just need to gather a list of keywords you can use to get traffic from various sources such as search engines, or with pay-per-click marketing.
Lets say you have chosen the acne niche. Youre targeting individuals who have acne and are desperate to get rid of it. You would probably want to start with seed keyword phrases like acne and pimples.
This would return keywords such as:
Get rid of acne
How to clear up acne
Get rid of a pimple
I use the Google Keyword Tool for this:
This tool is free, and it returns results directly from Googles own internal database of searches people have performed. Although no keyword tool is 100% accurate, Googles own data is likely to be the most accurate you will find.
Google will give you around 100 keywords. You can then dig deeper by taking some of the keywords it returns and using those as seed keywords to find more.
If you are creating a small niche site, you may want to focus on just a handful of keywords. In this case, the 100 keywords you originally find may be enough. If you want to create a large authority site, you will potentially want thousands of keywords. This will require you to continue digging, using some of the keywords you find as additional seeds.
Once you have a list of keywords, you need to analyze them. Not every keyword is going to be one you would want to focus on for SEO purposes. Some wont have enough traffic to make them worth the time, and others will have too much compe