My website is listed in top 10 search results when some of the long tails are searched on google. I want to know if they keep changing (the search results I mean) and what can I do to maintain that page rank.
Well, Make sure SEO is on going process. And now you're #1 page with some of your targeted keywords, but you need to know you have 100000++ competitors. So now think what you have to do.... I my suggestion keep it up what you're doing now...
if it is one particular page rank you are looking for then try updating the post with some new content.. or rather i should say keep doing on page optimisation..
You should keep adding quality content to your site. Quality content will be linked to by others and more links to internal pages is loved by the search engines.
Fresh and creative content is the best solution of it. Because now Google is giving the most high priority to it.