Firstly, you must have an insurable interest in the person whose life you want to insure. This means that their death would have a significant financial impact on you, such as a spouse, business partner, or dependent. You cannot simply take out a policy on a stranger or someone you don't have a close relationship with.
Secondly, you must obtain the consent of the person whose life will be insured. They need to be aware of and agree to the life insurance policy. The insurance company will require proof of this consent, usually through the applicant signing the policy documents. There is an exception for parents or guardians taking out a policy on a minor child, but otherwise, the insured person's consent is mandatory.