To prevent charges to your credit card on AWS Free Tier, you should regularly monitor your usage and ensure that you stay within the limits of the free tier. You can do this by checking the AWS Cost and Usage report, which provides detailed information about your usage and charges. Additionally, you should set up alerts to notify you when you are approaching or exceeding your free tier limits. You can set up these alerts in the AWS Budgets service. Also, you can remove or delete any unneeded resources or services.