The goal of this guide is to approach keyword research for SEO from it's roots and build toward the more technical aspects.
Keyword research is the practice of identifying which phrases are used on search engines when people are looking for information, and usually includes finding both the search volume and relative competitiveness of the terms.
Keyword research is a critical component for search engine optimization because when used correctly it provides a road map for both the design and execution of building websites and developing content.
Keywords are usually broken up and grouped based on the number of words within the query phrases. The more words in a keyword phrase usually the easier it is to rank for the term, since usually there is less relative competition.
The reason for all the "usually's" is that this not absolute, as is the case with most things, there are exceptions…
Here is an example of how keyword difficulty relative to long tail keywords versus head and body keywords usually works:
And here is an example where both the body and the long tail keywords are equally as competitive:
And here is the exception, where a long tail keyword is actually more difficult than the body:
The keyword difficulty data above was gathered using Moz's keyword difficulty tool on 1/5/13.
It's worth mentioning that in my experience, this really only ever happens with queries that contain brand names, 9 out of 10 long tail terms are going to be less difficult to rank for than their body and head counterparts.
For those of you unfamiliar with the idea of keyword difficulty, it is a lot like what it sounds like; a relative measure of how competitive it is within organic search results. A higher keyword difficulty score means that is going to be more difficult to gain high natural rankings than a keyword with a lower score.