Even before you hire an SEO to do some work on your website, you really need to know what you're getting for your hard earned money.
The great thing about SEO is that nearly all of it is trackable. Every website visitor leaves a nice trail when they come by, and over time you can collect that data and sort through it for patterns, good or bad. Then, armed with that data, you can make changes that increase the amount of clickthroughs, or even move things around on your page to help influence a higher purchase rate.
However, none of this is possible if you aren't collecting the data.
Google analytics is arguably one of the best (and free) analytics collection programs on the market today. Setting it up for your website is a breeze, just sign up and add the code they provide you to each page of your website.
This will do a couple of nice things for you, even before you hire an SEO to start spiffing up your site.
You'll set a baseline of visitors
You have to know what is already going on on your website before you hire an SEO. Knowing your baseline of visitors over a week or month will show you the impact of the things you have already done to promote your website. If it shows an average of 20 visitors a week, then you know that if it increases to 30 and then 40, that your SEO is actually doing things for you.
You can track landing pages
If you're really not into SEO, or not into marketing at all, chances are you are promoting your home page URL as the place to go. But what happens if your page on custom widgets is getting tons of traffic, and you had no idea? You may already have a great web page that doesn't have a good call to action, and you don't even know it!
You can see which search engine is referring traffic
Not sure if your visitors are coming from Yahoo!, MSN or Google? A good analytics program will tell you where your strong points are, helping your SEO focus on boosting those rankings and growing the others into a mature state as well.
You can see geo-information about your visitors
What if you're a blue widget maker who only sells in Missouri? And what if 85% of your visitors are living in Washington? It doesn't do you much good if you only sell to Missourians. Know where your current traffic is coming from, and adjust accordingly.
I know this post is a bit down-n-dirty, but I hope I've made the idea clear. Go get signed up for Google Analytics today. Get it set up on your account, and then start looking for a good SEO company to help you improve your baseline.