How do I stop my canon selphy cp1300 from printing out dull looking pictures?

The problem is probably a mix between a lack of understanding and a mismatch of monitor calibration.

I have the very same printer and use it as a low end printer to fabricate water resistant prints.

Understanding the difference between monitor and print

While a monitor image is emitting light by itself, the printed image can only be a light as the reflected light of the paper medium. This means that most images are far less brighter than on the screen. If you want to achieve a good print, you will have to optimize the photo for printing.

Additionally some colors cannot easily be reproduced by the 4 standard printing colors (cyan magenta yellow and black). Expensive specialized photo printers use more than these 4 colors to help the printing process for better color rendition.

Monitor settings

Most consumer monitors are set way too bright and the color contrast is set quite harsh. If you optimize an image on a monitor with these settings, the image will look more colorful and brighter than it really is. If you print it, you will see the mismatch very clearly.

You could use a professional colorimeter to calibrate your monitor, but there is a cheaper way, which might help in your case. Go into the settings of the printer and switch color optimization off. Then print a colorful image of you choice. Make sure it is a sRGB jpg. Now take the print, and try to set the brightness of the monitor so that ii is a bit similiar to the image. If the colors are very off, see if you can achieve a better match with the contrast settings.

Now see what you can achieve by editing the image and saving it as a sRBG jpg. If you edit it to be colorful and print it now, it should be closer to what you are getting.

However, the printer is a low end consumer device. The quality is about the same as the prints you get from a drug store or instant printing service.

Other color spaces

You should absolutely make sure that the images are in the SRGB color space (that is the base space for images on the web). Other stuff would be Adobe RGB, ProPhoto RGB and CMYK. These will be converted, with a loss of color rendition. I do not think, that this is the problem here, though.

Your printer does not have its own adjustments. It is not possible to balance the image on the camera with the print unless you use an external software to do the printing. For example, you must load the image into Photoshop and set the interface to let Photoshop manage colors. You can then make your the adjustments to the image and print with more control.