Right keyword choice is one of the most important SEO aspects many webmasters still neglect. Choosing the right keyword to rank for will determine success of your website. If you fail on this stage you will end up losing your time and money.
At first you should look at tendencies of what people search. You can type your keyword in Google keyword tool and see how many people actually searching your keyword.
Let's say you have found keywords which have around few thousands searches a day that doesn't mean that you should choose those keywords. You should analyze your competition at that point. While having a keyword with few thousands of searches a day is great it won't be that great if in order to get to the top positions (by top positions i mean page one of search engines ) you will have to outrank sites like Wikipedia, BBC etc. It will be a waste of your money.
So if you are unable to beat competition at the page one you should pick another keyword.
On the other hand if you see on the page one of search engines sites with few articles, bad looking websites - you can go with your keyword.
But don't try to look only for keywords which have thousands searches a day. Even keywords which have few thousands searches a month can do well.
On the other hand if you will pick keyword which has about 300 searches a month you will probably not make any money, because nobody is searching for it.