I started root canal a year ago but haven't completed it yet what precaution can I take to avoid disease at present. It isnt causing me any problem?

Wait and watch. An root canal should be finished in close proximity to the time that it was started. Leaving it half completed is like waiting for the time bomb to go off. Since the nerve is no longer present, chances are the pain is less, but the source of the original infection is probably still present. See your dentist asap.
Dentist can re-check. A person who started a root canal but did not finish, may or may not have a temporary crown on the tooth. The tooth may be more likely to crack or break if it is not properly crowned. It may be more likely to get decay if it is not protected and sealed off from the bacteria and food substances. It is best to check with a dentist to get the tooth well-protected.