i have never thought much about using my rss feed for promotion but now I am looking for ways to utilize it
You can create a page or a post on your site titled something on the lines of why you should subscribe to my RSS and highlight the benefits and motivations for people to subscribe to your RSS feed, just an idea, hope it helps.
i think rss is your information source whereby people can catch you with your site and if they like your site they can subscribe in your rss feed and they wil get mail when u change something in your site, if anything wrong
If you constantly update your website i.e. you publish articles or news or have got a product catalog and keep changing things, then RSS is a must because this is the way subscribing people can know that you have updated your website.