I have blogspot blog target for minor keywords(low competition keyword) for those keywords it was ranking on first page, but I change the meta tags of the blog and suddenly ranking fall down, still i work on off page for that blog but still blog lost the ranking completely, not even seen in search engine, then again I restore the previous meta tags on which blog was ranking but still the ranking is not back. Please help me in this matter what should i do to get back the ranking.
Go back to how it originally was (meta tags.) Then keep posting content, you'll regain your position.
It's going to be very difficult to give you an answer without knowing what the serp is. My initial response is that you will often see a new webpage rank very well for a serp at first, and then fall down in position to where it's natural position should be. That could be the case here. Also, for each change in the meta title of your page, you should wait at least 2 or 3 weeks to realize the full effect.