Google Alerts are a handy way to receive updates on newly indexed content on topics / keywords of your choosing. Updates are sent via email, at a frequency you choose. Go to http://google.com/alerts to get started.
For example, if you have a site about dog booties, you might set up alerts for things like “dog clothing”, “dog booties”, information about specific breeds, etc. It allows you to see what kind of content other people are creating and how you might adopt some of those ideas or use them for commentary on your own site.
All you do is fill in the form to set up an alert or if you log into your Google account, you can manage them from there.