You can talk to any SEO company in the world, and they’ll all offer you the same basic concept: they’ll build backlinks for you, and raise your page’s ranking in the Search Engine Results Pages (SERPs). But that’s a very simplistic idea, because it leaves out the complex truth behind what Search Engine Optimization does — and doesn’t — do.
SEO, when done well, will absolutely get your page ranked in the SERPs, but you don’t rank “on Google”. You rank for a specific keyword or phrase on Google. If you just haphazardly build backlinks to your page, sure, you’ll end up ranking for something — but what exactly that ‘something’ is isn’t under your control. It’s dependent on a combination of your on-page SEO, your content, your anchor texts, and the content of the pages you backlink from.
On the other hand, if you find someone to do solid keyword research for you, and you understand that SEO is, in the end, keyword-centric and not site- or engine-centric, you can (re)build your pages from the ground up to focus on the keywords you’re SEOing towards. The next realization you need to have is that not all keywords are equal.
Most many daily searches, how many competing pages, etc. Some will go a step further and tell you about the competition in more detail, telling you how many backlinks and of what quality they have, giving you a chance to determine how difficult it will be to conquer that keyword. But that’s not everything either.
Keywords aren’t just entities that search engines use to determine SERPs rankings. They’re human language, and like all human language, keywords have their own inherent 
context. That context can have profound impacts on your business. For example, if you could go after “free aquarium construction” or “how to build a high quality aquarium”, which would you? Exactly — you’d avoid the word “free” because it’s a dead giveaway that that person isn’t spending money if they can avoid it.
Now choose between “affordable SEO services” and “backlinking campaigns”. It’s a little harder, but the word “affordable” is a sure giveaway that the person who typed that in has money and wants to spend it — if carefully — on some SEO. The other person is probably just looking for information.
It’s small but important things like this that separate a highly effective SEO job with a mediocre one. It all starts — it ALL starts — with the right keywords.
