I put a sitemap on every site I do now.
For example:
http://www.restaurant-business-planning.com/sitemap.xml
What you should do is use google webmaster tools as well:
https://www.google.com/webmasters/tools/
You then submit your sitemap in the tools - by doing this you'll get the search engine spider that matters to your site. You'll get lots of data as well such as what terms have been searched, page views etc. as well as any errors which need fixing.
If you look at my sitemap above it just gives the page address and the priority of each page - which I created manually(to a degree :-)) There are other things you can put in there such as:
<lastmod>2008-01-01</lastmod>
<changefreq>weekly</changefreq>
I'm not entirely sure how important these are in terms of if google actually uses that info.
I would also point to your sitemap in your robots file:
e.g.
User-agent: Mediapartners-Google*
User-agent: *
Sitemap:
http://www.restaurant-business-planning.com/sitemap.xml