Hi All, I would like to get expert advice on this problem. I have changed one of my domains recently and pointed the old website to the new domain. All 301 redirection rule has been added in the .htaccess of old domain. Also changed the setting in Google webmaster account. But I could find a recent ranking dropping for this website. What will be the reason for the same. Any thing else to be implemented for this website? Any tips to retain the ranking?
There will be a definite change in ranking, downwards if I may say so, however that doesn't also mean that you can't get back up. Simply continue doing all SEO stuffs that you've been doing (assuming that what you're doing are all white hat SEO) on the new domain URL you have now redirected to. Just be sure that you really have implemented a 301 permanent redirection and not 302 temporary redirection.
Google will take sometime before it recognizes and starts transferring over the same repute your old domain had
By saying shutting down a web site and redirecting its domain to the other one is a great loss of link juices shared internally. Though 301 might help with passing some of the link juices the domain acquires from the sources that links to it.