Think of a keyword as the key to unlock the internet.
This opens the door to all possibilities, you could have people flocking to your door if you do this right.
So think of your niche and what the main subjects are. If you are into cooking then recipes are important, if you are into dancing then styles are important, if you are into online marketing then occupations could be important.
Lets take a niche and find a keyword. We are looking for low hanging fruit. These are keywords that have hardly any competition for them. If you type 'car' you will have a big problem in getting ranked with such a huge market the competition will be intensely fierce. It is so generic that every man and his dog will be using that word and you won't even get a look in.
So let's say you have a niche in hairdressing. We can type this into our search tool and see what comes up. I will be using Jaaxy for speed and convenience
As you can see, it's a well used keyword and there doesn't appear to be any really low hanging fruit here.
Headings from left to right; 1. Keyword. 2 Average search traffic per month. 3. Traffic you may get if you are on page one. 4. The competing websites. 5. Quality indicator from green(great) to red(abysmal) 6. The higher the score here the more likely you will get ranked higher. 7. Domains available if you use the keywords suggested. 8. The related keywords. 9. Brainstorm - try it and see what you get.