Look for a graphic like this image on the web page. It may also appear in the address bar and sometimes other graphics are used - here's a few more you may come across.
Some sites will have a link for RSS feeds at the bottom/footer of their home page - this usually takes you to a page with a variety of feeds to choose from.
Look for terms like "alerts", "follow us", "subscribe", "news" or "site updates" (often on the right side or at the bottom of a page). If you don't see anything try using the site search for "RSS" or any of these terms.