What to expect from your SEO
To begin with, as we have had in our contracts since we began, SEO is not a science, but an art (or words to that effect). There are definitely known factors which influence ranking - the <Title> tag, <H1> tag (and through H6), bolding text, keywords in the first sentence and a bunch of others. That's on-page SEO and it's somewhat quantifiable. I say somewhat, because, with Google, the goal posts are continually moving. Content "above the fold" is a hot change this year. Many sites have rightly recognised this as prime advertising real estate and jammed it full of ads. Google says, "No, our surfer came to learn about <search phrase>, why should they be assaulted with ads?" So these sites have received a penalty.
Off-page SEO is as fluid as on-page. Link farms and link sites were hit hard this year. The traditional reign of back links has been diminished somewhat (though are still important) with more weight going onto social bookmarking.
Magician or artiste?
What is your expectation of your SEO person? Have they set your expectations properly? Do you see them as Merlin, ready to wave a magic wand (knowing all the "inside" secrets), and, "poof", your ranking blues are gone? Or do you understand that, done correctly (that is, white hat as opposed to black hat), SEO takes time plus constant checking? Less competitive keyphrases can be ranked reasonably quickly, but, where the competition is more fierce, it can take months or years - sometimes the competition is so entrenched it can be virtually impossible.
Diversify your reach
Whilst an online presence is pretty much mandatory now, don't put all your eggs in one basket. Any marketing person will tell you that advertising should be focused and measured, but it shouldn't be limited to one realm or medium. Get a website, keep fresh content on it, but don't neglect other methods - phone directories, paper, radio, TV, magazines, flyers, etc. And don't forget QR codes on all your printed material.
Ranking v Traffic
On the face of it, it would seem that no ranking = no traffic. And that's mostly correct; especially for a new site. However, the latest round of Google updates have produced some strange results. For our own site, we have seen some significant drops in rankings for some phrases, yet our traffic volumes remain unchanged. And I have read of webmasters lamenting that their rankings have increased, but traffic has remained unchanged. In one case, their traffic decreased! As I said, SEO is not an exact science.