Sounds as though you might need to increase contrast and maybe saturation before printing. You should start by making a copy of your image file and add "_Print" at the end. Things to try (with the image in proof) are
Flatten the image (or click top layer then shift+cntrl+alt+e to create a new layer with the others merged in)
Try applying some Unsharp mask using values of amount=20, radius=40 (can vary these, I find radius 2 times amount a good starting point - with amounts between 15 and 40 being quite useable).
To add some saturation or reduce saturation to remove out of gamut colours, then create a "selective colour" layer
Select a colour from the drop down menu, then use the bottom slider (called black in CS3) to darken brighten (-ve values) the colour. You can also adjust the mix of other colours in there and selecting the same slider as the colour in the drop down makes it more or less intense (same as a hue/saturation layer). Work through the colours - the bottom slider has little effect then just move on to the next - not all images are rich in all colours. The "selective colour" layer is one of the most versatile options for adjusting colours, worth getting to know it.
A simple approach - sometimes works, sometimes not - is to create a curves layer but do not adjust the curve - just click OK. Set the blending mode to "soft light" then reduce opacity to 20% to 60% depending on how strong an effect you want. You can also adjust the curve to target the effect a little.
Just a few thoughts