The first thing you need to decide is how to add the second person. Will it be as an authorized user or a co-signer? An authorized user is not legally responsible to make payments on the credit card purchases on the account, while a co-signer is.
For parents who want to help their children build credit, getting a shared credit card where the children are authorized users may be ideal. The same purpose can apply to a spouse who needs help in improving credit rating. Just confirm with the bank if it reports the activity of the authorized users to the credit bureaus to achieve your purpose.
Meanwhile, co-signers or having joint accounts are more common in relationships that involve equal financial responsibilities. You need to apply for this and create a new shared account where you share both the benefits and responsibilities. This works best if both account holders have similar spending habits and financial goals.
For more information visit: Best Tips for Sharing a Credit Card