One of the proven ways to get SEO without dipping into black hat SEO (which will almost certainly get you nailed by a Google update at some point in the not-too-distant future) is to produce great content.
Even if you have the ability within your team to produce great content, though, great content is a creative activity that takes time and space. Let's say you have a Paul Graham on your team, who can write amazing awesome articles on a fairly regular basis. He still will only be able to write a few of those a month at best (probably less). Push your Paul-Graham-junior to write one article a day, and quality will drop rapidly.
So, how do you scale great content?
The secret is earth-shattering: you hire great writers outside your team. How do you find them? How do you approach them? How do you use them?
Check out this very thorough guide by Matthew Barby of reputable Moz.com for the answers.