If you're struggling to think of more keywords people might be searching about a specific topic, go to Google.com and take a look at the related search terms that appear when you plug in a keyword. When you type in your phrase and scroll to the bottom of Google's results, you'll notice some suggestions for searches related to your original input. These keywords can spark ideas for other keywords you may want to take into consideration.
You don’t really need to worry about the volume size either. Too big a number just means you will have to work harder to get ranked in Google. It’s now quite commonplace to see SEO people say it’s best to just go with your gut feeling on a keyword. Just go for something you would type into Google search yourself instead of beating yourself up trying to find that ‘one’ killer keyword.
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.