3. Set your pre-search filters. Depending on whether you are looking for a new niche to build a site around or trying to find keywords to target on your already existing website, the minimum amount of local monthly searches (LMS) you set might vary. For new niches my LMS criteria is 1,500-5,000 searches, for posts anything from 10-800 is fine. Also, depending on one of these goals you can add a lower or higher number of words in the respective filter: for new niches 3 (or, at times, 2) words minimum, for new posts from 3 or 4 words up.
Because great content requires a deep understanding of the main idea (e.g., “ac repair houston”) and the supporting subtopics that require coverage (e.g., “central ac vs portable ac systems”) and the common issues that users seek answers for (e.g., “freon,” “refrigeration loops,” “coolant refills,” “troubleshooting”), the effectiveness of a keyword reporting tool is only as strong as the SEO pro using it.
Given you have a good idea of where to start and are fairly confident you are speaking the same language as your client, jump start research by generating related keyphrases and long tail variants with the ever so easy to use Google Autocomplete. This tool makes predictions based on what you are typing that are a reflection of Google search activity.
In addition, you can dig into the paid side of search and find out what keywords your competitors are bidding on, and then leverage those keywords for your own organic benefit if you're not already doing so. Search Metrics does this as well, but I've found SEMRush to provide a greater range of keywords and they save more historical keyword data than Search Metrics.
Long tail keywords can find people who are later in the buying cycle, and more ready to buy. For example, somebody searching for “tents” is probably early in the buying cycle, just starting to research what they want. Whereas somebody who searches for “North Face Kaiju 4 person tent” already knows what they want, and is more likely to be ready to buy.
Long Tail Pro is a keyword research tool that helps you quickly find low competition keywords for your website.  In particular, the tool is built for people doing SEO (search engine optimization) as opposed to people doing paid ads (Google Adwords PPC).  I'm sure there are some advertisers that use the tool for paid ad keyword research, but the tool was built for SEO keyword research.