This is basically about arena footing, but a lot of the common sense basics should apply to all riding, including riding on the trail. Again, you'll have to login in www.thehorse.com to see the article, but the subscription is free.
http://thehorse.com/ViewArticle.aspx?ID=187&kw=arena%20footing Moderation seems to be the key...note that "ice" isn't even mentioned as a "footing." Karen Thomas, NC