How are you resizing the images from your camera? Many download at only 72ppi, which is a very poor resolution, especially for printing. Also, most are downloaded as JPEGs, which is known as a "lossy" format. If you're working with 72ppi images and editing and saving the changes, you'll be losing image quality.
Briefly, the best workflow is to immediately do a Save As and convert to a non-lossy format, such as PSD or TIFF, and then to do resizing in the Image>Resize>Image Size dialog box. Experiment with increasing the resolution until you get a size close to the 4 X 6 you're after, and always work with the Resample Box unchecked. Many cameras, mine included, shoot images at an aspect ratio that will not equal a perfect 4 X 6 without some minor cropping.
If you'll post some additional information about the size, format, and resolution of the images as they come from your camera, someone will be able to give you some pointers on how to go about resizing without a loss of quality, e.g., getting pixeled pictures.