I do the same thing. A picture shows up lighter than it actually is on my monitor, so I lighten it up in Photoshop, then my printer allows me to lighten up the print more in the process. It's harder to maintain control when you aren't printing them out yourself, though.

This probably won't be much help but:

I always lighten my photos quite a bit more than I would want because you need to allow for the printer printing the photos darker than it looks on the screen.

I ordered from Snapfish to pick up at Walgreens. When I got home I noticed that they were ALOT darker than the original. What should I do? I've heard some people lighten them up before printing? Please help!