There is no magic bullet when it comes to SEO. SEO success depends on a variety of onsite and offsite SEO. For onsite, having rich content that your USERS want to see is critical. Long gone are the days where blogs are optional on a website — they’re mandatory.
Keywords themselves aren’t as important — Google’s algorithms are more robust than ever, so the engines can tell that “salesman” is the same as “sales person” “saleswoman” “sales professional”, etc. (Semantic search is big right now, so if you’re targeting a keyword/keyword phrase, think of synonyms for those keywords.)
While we’re on the topic of keywords, don’t pick generic keywords — go for the keywords with buyer intent (target “Bose Wireless Headphones” vs. “wireless headphones” — why? Because if you’re selling Bose Wireless Headphones and someone is searching for that specific term, chances are they’ve already done their research and they’re ready to buy.)
Off-site things that are important are claiming (AND optimizing) your Google My Business page, Google+ Business page, Bing Places for Business, Yahoo! Local and make sure you’re listed correctly/consistently on the 100+ other online business directories that show up in search engine results pages (SERPs).
Linking is crucial these days — that is, high quality websites linking to YOUR website. That is a time consuming task, and you definitely want to be careful who links to your site.
I like to say that an SEO professional has a whole arsenal of strategies that are customizable to YOUR website ranking needs. If you find a “one size fits all” SEO agency or an agency that only charges a few hundred dollars for their services, something’s up (i.e. not right). Professional SEO takes time — LOTS of it — so if someone is doing it on the cheap, chances are they’re doing something wrong that could potentially get your site blacklisted (i.e. taken off Google’s radar altogether).