At that time I haven't update regarding drinking & smoking as I think I smoke occasionally at that time.
You have provided wrong info at the time of buying policy.

Now I smoke 2 to 3 cigarettes per day. And drink occasionally
This post must have cleared your doubt -
"If you are in any doubt as to whether a fact is material then it should be disclosed. If any changes in circumstances arise during the period of insurance cover please provide details."

Another question is that I am planning to take one new term policy from LIC. Agent told me that no need to declare about smoking and drinking if you smoke 2 or 3 cigrattess. So it is fine if I am not going to declare about smoking in form. Otherwise there might be possibility if my application reject.
It's upto you to decide what you want to disclose on the proposal form. My personal opinion is always give right information if asked in the proposal form.