Don’t underestimate these less popular keywords. Long tail keywords with lower search volume often convert better, because searchers are more specific and intentional in their searches. For example, a person searching for "shoes" is probably just browsing. On the other hand, someone searching for "best price red womens size 7 running shoe" practically has their wallet out!
The errors in technical SEO are often not obvious, and therefore one of the most popular. Mistakes in robots.txt and 404 pages, pagination and canonical URLs, hreflang tags and 301 redirects, http vs https and www vs non www versions: each of them can seriously spoil all efforts to promote the site. One quality SEO website analysis is enough to solve all the main problems in this part forever.
QUOTE: “If an off-domain link is made by an anonymous or unauthenticated user, I’d use nofollow on that link. Once a user has done a certain number of posts/edits, or has been around for long enough to build up trust, then those nofollows could be removed and the links could be trusted. Anytime you have a user that you’d trust, there’s no need to use nofollow links.” Matt Cutts, Google 2006
Ask for a technical and search audit for your site to learn what they think needs to be done, why, and what the expected outcome should be. You'll probably have to pay for this. You will probably have to give them read-only access to your site on Search Console. (At this stage, don't grant them write access.) Your prospective SEO should be able to give you realistic estimates of improvement, and an estimate of the work involved. If they guarantee you that their changes will give you first place in search results, find someone else.