Hire an experienced professional who can market your website.  You wouldn’t hire a auto mechanic to perform heart surgery would you?  Treat your website like the valuable marketing vehicle it is by entrusting its promotion to someone who knows what to do and how to accomplish your goals. 

If you’re looking to perform SEO in-house, look for a firm that offers training or some sort of combination of doing the work while educating your personnel along the way so they can take over the repetitive nature tasks at some point.  Better firms will not have much of an issue with this approach.

Remember to run the other way if someone guarantees a top ranking in any of the search engines however.  As you have likely read numerous times, organic search engine rankings are dynamic and cannot be purchased.   

As with any service you’re considering an external resource to perform, do a little background research on the firms.  Reputable firms will have testimonials and case studies to review along with live customers you can chat with to find out how well they’ve performed and how easy they’ve been to work with.