It’s quite easy to rank at the top of the search engines for words and phrases that aren't competitive. However, the difficulty is in deciding what keywords are going to drive not only a significant amount of traffic but also the traffic that is most likely to convert visitors into customers/subscribers/contacts etc.
It is important though, to consider the balance between what keywords are going to drive traffic and what keywords are going to be so competitive that it will be almost impossible to rank on the first page.
I can’t stress enough how important it is to take part in some keyword research even prior to deciding what navigation structure to use on a website. Knowing which keywords will drive traffic should be one of the things that help a website owner to decide what content will be included but more often than not website owners do the opposite and create content that simply won’t drive traffic.
The following tools are great resources for keyword research discovery and while they don’t give exact numbers, are vital for researching keywords: