Here are some of the quick fixes I have used
Make sure your printer is set to the Best setting, and photo quality paper.
Make sure you are taking digital pics you want to blow up on the Best resolution on your camera. It may be that you are using the lowest setting on the camera and therefore the print will be grainy when blown up. I always set it to the highest setting unless its for a pic for ebay or something.
I print all my own pics on my HP 2210 and love it!!!!! I have taken them to the local photo store and they don't do as good of a job as my printer does. I love it!!!
Paper is a big concern too....I use only the premium quality or better, mostly high gloss. I have blown up many pics, even for some contests!!!
I would take back the printer if I wasn't happy with it.
hope I helped a little
cindy