Recently I have noticed a drastic dip in all the major keyword of my site.Most of them were in the top ten for about the period of 11 months.I am not able to figure out a reason for this can anyone help of what to do for getting the rankings back.

It should be back to normal, wait for a week or two, if it is not back, it could have hit with some filter, try your backlinking with a different set of keywords, and IP diversity is the key. Also it is good to try backlinking your deeplinks

If your website experiences a sudden fall in ranking for its main keywords, it may have been caused only by an Google algorithm change such as the recent Panda update or by periodic organic search results (SERP) churn.