There are multiple ways to identify low-hanging fruit keywords. One of the simplest ways is by filtering the keywords that are currently ranking in position 4-10 or 11-20 in Rank Intelligence (pictured below), Research Grid or Search Analytics. This will help to identify content topics that perform (rank) well already and with some work could improve into a better top ranking position (and improve search visibility). 

From our blog: Understand and Manage Keyword Performance

Another approach to identifying low hanging keyword opportunities is by reviewing the Keyword Difficulty (pictured below in Keyword Detail). The difficulty score helps to prioritize which keywords to invest time and effort in first. Learn More

From our blog: Keyword Difficulty and Its Role in Prioritizing Keyword Opportunities