I come from photography, not graphic design, so I won't be completely correct, but this could be a start. If your monitor is not calibrated what you see on screen will very likely not be what comes out of the printer. I expect the same thing about printer calibration, but I have never gone down that road. The cheap way to see where your problems are is to buy a pantone color swatch from a photo store. Paint or draw with the colors (by entering RGB or CMYK numbers) and see how close the colors look on screen and out of the printer to the swatch. That should tell you where your problems are.