You need to redirect people to HTTPS, and your credit card form should have a secure lock icon as well as icons for the credit cards you accept. You should have a little promise on your form like "Your credit card information is encrypted for your protection by Industry-Grade 256bit Encryption and will never be shared."

As far as the rest of your website, for me personally, I trust websites that are polished, simple, and have professional copy. I was really impressed with Swipe.com recently and immediately trusted them.