Becoming an authorized user on someone else's credit card or adding an authorized user to your credit card is an easy way to give your credit score a boost. For married couples and long-term partners, this move is a no-brainer. You can both improve your credit scores just by signing on as an authorized user of each other's credit cards. Lenders look at cardholders who are authorized users differently because they are different. Statistically, cardholders who are trusted by friends, family members and partners are more reliable borrowers, which earns them a small boost to their credit score.
What can and DOES change is whether you have a collector pursuing you for the debt. If you are talking about a dormant account that has been in collections and has finally been left alone with no collections activity for a few years, messing with it can be problematic from the point of view that the collections people will start pestering you again to see if they can get money and if the SOL isn't up, they can start reporting on it again which can affect your score or they could even file suit if your state SOL isn't up.
Making your credit payments on time is one of the biggest contributing factors to your credit scores. Some banks offer payment reminders through their online banking portals that can send you an email or text message reminding you when a payment is due. You could also consider enrolling in automatic payments through your credit card and loan providers to have payments automatically debited from your bank account, but this only makes the minimum payment on your credit cards and does not help instill a sense of money management.