A grey card is a valuable tool for setting a good exposure and for setting the correct white-balance in editing software. Use a low ISO like 100 for the least digital noise, a middle-aperture like f8 to get the best sharpness from your lens, and then pick the shutter speed that centers the exposure needle. Low shutter speeds are fine because your camera is not hand-held and your subject isn’t moving.
Shoot RAW for the most flexibility, but if you are confident with your exposures and white-balance, shooting JPEG will save a lot of time and require simpler software.
Better still is to use a color-calibration tool like the Spyder Checkr. This matches a calibrated color-swatch to the pixel readouts on your computer monitor for the most accurate color reproduction of your work. It will save a lot of printer ink compared to a trial and error method.
Light sources can be tricky so remember these concepts:
The farther away the light-source the more even it will light your work. A well lit-room usually works, but setting up continuous or strobe lighting gives you more control.
The larger the light-source relative to the work the more gradational the transition from highlight to shadow.
Like in billiards, the angle of incidence equals the angle of reflection. Have the light angled so it doesn’t reflect straight back into the camera. A 45 degree angle to the camera is a great place to start.
For even light, use a light source both left and right of the work, the same distance and power setting.
If you want a more textured result, lower the lights so the light skims across the surface of the work, and play with altering the relative power of just one of the two lights. The relative orientation of the relief in your piece and the lights will make a big difference.
If the work is behind glass, remove the glass from the frame to prevent unnecessary glare or reflections. If you are competent with vector-graphic software like Affinity Design or Adobe Illustrator, you can mock-up a mat or a frame so that you can create a digital final-product image rather than mount all your work by hand. See the images in my Print Store as an example.
Processing
A good print starts with an accurate representation of your scan on your computer screen. You can calibrate your monitor for accurate color using a tool such as these from Datacolor and Calibrite.
A good global edit usually means setting your brightness slider so that the histogram is centered. Then set the black and white points so that are almost, but not quite, clipping. Of course, if you have a very dark, or very bright piece of work, your histogram should reflect that. Most software have lens-correction and perspective-correction tools to make sure the angular relationships in the final image honor that of the original piece.
Crop the image to the edge of the artwork, or to a desired aspect ratio for printing. If you are matting the prints, you’ll have to use a standard aspect ratio to fit store-bought matts or you can make custom mats to best honor your art.
You can use local editing tools like a spot healer to remove any dust or a gradient tool to remove any uneven light. I’d avoid removing imperfections of the artwork itself as you want to avoid misrepresenting your work to your buyer.
Printing