Especially for smaller brands
According to Baymard, 18% of shoppers (from 1044 respondents in US) abandon their cart because they do not trust the site with their credit card information. The tips below are especially important if your store is NOT a large brand such as Apple, Microsoft or Walmart.
Trust seals, padlocks, and more
Encapsulate the credit card fields with a solid background color to make it look more secure than the rest of the form fields that require less sensitive information.
Place your (real) 3rd party trust seal(s) close to the credit card fields.
Alternatively, add a homemade padlock icon or two in the encapsulated credit card section. It can for example be placed in the header of the credit card section, or next to the credit card number field. They have been observed to perform better than 3rd party trust seals.
Test your checkout form thoroughly and make sure it has no layout bugs and works perfectly, as any problem with it can completely remove all sense of security for shoppers.