The “Starter” tier, with 1000 keyword lookups every 24 hours should be enough for anyone starting out in blogging – or even people who are quite established. It’s pleasing to see a product where they don’t seem to trick you into having to pay for a more expensive version. On the more negative side, I did feel that you’re nudged towards doing annual payment, with the monthly option kept slightly “hidden.”
If you go to Search Console under the Acquisition tab and then click Queries, you’ll be able to see different searches (aka keywords) that users found you through. You may have to set this up, but it’s easy to do and only takes a few minutes; you can see how here. Use this information to evaluate and monitor your keywords to see what’s working and what needs to be changed.

Successful SEO requires multiple interrelated activities on all fronts: competition, keywords, link building, on-page and technical optimization. It creates a need for diverse tools, which is expensive. SEMrush solves this problem with an award-winning all-in-one toolkit that includes 17 tools covering all SEO fields. We’ll walk you through your SEO workflow, explaining how to get the most out of our toolkit.
I love Moz’s interface and how they give you data on the keywords. It’s easy-to-read, making it an ideal solution for both experts and newbies alike. They’ll show you both numeric and visual representations of a keyword’s monthly search volume, its opportunity for ranking, priority, and difficulty. They’ll also show you keyword suggestions and SERP analysis, which is fantastic and detailed.
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.