You can use Google’s free search tool to find keywords, defined as long-tail phrases that are highly valuable for your niche. For example, if you were an affiliate marketer in the skateboarding industry, a keyword might be “electric skateboard wheels”. When you type the phrase into Google and select the Search Tools button on the right side of the screen, you’ll see a panel below your search input fields that has several options related to conversion conversions – including “Ad Group Ideas”, where internet marketers enter a word or phrase to generate hundreds of ad group ideas.
You can also use Explore Keywords’ free keywords tools including

1. Keyword Volume Checker
2. Keywords for Bloggers
3. Keywords for YouTubers
4. Keywords for eCommerce