Google AdWords Keyword Planner
Of course, Google has always been a premiere research tool and there are a few news ones that you can use that are pretty good the Google tool still remains a constant.
The traditional approach is to use the planner by entering a few "seed" words and then the planner will come up with some more suggestions for you, together with estimates of traffic volume, and an indication of how competitive (or difficult to rank for) each keyword is. But since everyone sees the same results and then targets the same keywords, including your competition.Also, as of January 2017 they now require you to have an Adwords account to get the detailed numbers for the keyword search that you do but it shows search volume data in approximate ranges.
Here's an excerpt from an article by: Ankit Singal,