1) Submit your sites and urls using webmaster tools. Just hit this -> Submit URLs to Google with Fetch as Googlebot
2) Submit a site map to webmaster tools. Just hit this -> Submit a sitemap It takes a short time, it's easy to do and will make a MASSIVE difference to your sites visibility.
3) redirect your naked domain name - check out Redirect Your Naked Domain Using wwwizer
Check out this SEO guide written just for google sites here:
SEO Guide by steegle
Get to webmaster tools here:
Be warned however if you have a custom domain eg yoursite.com make sure you submit that to the index not your sites.google.com/site/yoursite url or your GS url might be riding higher than your custom domain!
There's no magic wand but with time and effort you'll get the visitors you need.
Google Analytics allows you to actually check your progress. Get it here:
Adwords is a great way to advertising your website too. buy adwords here:
Adwords - Pay Per Click Advertising
Also keep your site's content kept fresh by getting an announcements page:
Like a blog, an announcement page display posts you create. you could use it as a news page, to record meeting notes and agendas, as an online journal or just to keep your site users wanting to come back for more .... I can't stress how important it is to post, just once a week .... To get hits why wouldn't you?
Ps - Let me know how you get on.