You can use tools to find the right keywords.
Did you know that there are levels of keywords?
This is usually done using a keyword generator, it attempts to generate a list of keywords that you can use to begin to develop a list of effective keywords and keyword phrases.
A phrase is a combination of words that when put together, have an extended meaning for the user.
Sometimes these can be called long tail keywords, which might or might not be helpful.
However if you can find a way to really match those long tail searches with consumers looking for your product, then you can find a really great method of converting those visitors into paying customers.
For example lets take the Automotive niche, if you have a website that deals with Automotive repair, then you can create the best fit for your content and your keywords.
When you do that, then you can develop that level of consumer trust that you need in order to be successful.