Hi Heather!
Color calibration is definitely not an exact science! This is such a broad and often confusing topic, but the best advice I can give is to make sure you at least calibrate your monitor using a utility like Adobe Gamma.
Second, since you use an online printer, it would be a good idea to find out if they have any preferences as far as what color space to use. I could not find much info as far as color matching on the Ofoto site, so you might need to email them.
Lastly, there are several good, informative threads on this site where you can find lots of excellent info on calibration.
monitor callibration more callibration...
I'm probably leaving out some...but also try the Adobe website and this
site has some good info. I'm sure there are lots more!
Hope that helps a little.
