The most important part in the proposal form is the details of medical history of the proposer and his family. Based on this information the insurer will arrive at the premium to be charged and whether the policy can be issued or not. Disclose all the relevant facts in this regard as well as habits pertaining to consumption of alcohol and tobacco.
Furnish the correct information regarding your age, height, weight, occupation, income, existing policy details and any other details asked in the form.
Often people do not reveal the details of other policies they hold since it takes time and requires some effort to gather the details of existing insurance policies.
Be honest. It will hold you in good stead.