Google Search Console (formerly Webmaster Tools) is one of the best SEO tools out there, and it's 100% free.
If you haven't already, go sign up for it here. (Tip: the "Google Analytics" ownership verification method is usually easiest.)
Search Console lets you see a whole lot about your site's health and performance from an SEO standpoint, but one of my favorite things to do with it is find opportunities for more traffic from long-tail keywords.
It's easy to do. Once you're signed up for Search Console, it only takes five minutes.
In Search Console, start by going to Search Traffic -> Search Analytics.
Then check the boxes for Clicks and Impressions, and select "Queries".
Scroll down to see a list of actual keyword phrases people are typing into Google to find your site.
The most popular query or two will usually be your brand, no surprise.
But look further down and you'll start to see phrases you'll be surprised by. These "Oh, I'm getting traffic from that?" keywords are easy opportunities to score more traffic from Google. Especially the ones with a lot of impressions.
When you see a keyword like that, just click the link icon next to it to see which page on your site is ranking for it, and then check whether that page actually has that exact phrase anywhere in the copy.
If it doesn't, write the phrase into the page copy somewhere. Now you're almost guaranteed to get more traffic from it going forward.