Here is a function that will hide a list from search. This way custom lists created won’t be included in search results.
If you notice the pages library is excluded. You don’t usually want to hide your content pages.
public static void ListHideFromSearch(SPList listToHide)
//Don’t ever hide the pages library
if (listToHide.Title.ToLower() != “pages”)
//Hide the list from search
listToHide.NoCrawl = true;
Here is a blog post about how to accomplish this same thing through the UI.