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.
These are usually single-word keywords with insane amounts of search volume and competition (for example, “insurance” or “vitamins”). Because searcher intent is all over the place (someone searching for “insurance” might be looking for a car insurance quote, a list of life insurance companies or a definition of the word), Head Terms usually don’t convert very well.
Long Tail Pro is a very useful piece of software for long tail keyword research. One of its best features is that you can carry out heavy analysis on the keywords of your choice, without being limited to only working with one or two at a time. It can provide you also with vast numbers of longtail keywords, or you can apply filters to find the precise keywords to fit your bill. And you can check your rankings at the same time!
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.