A common starting setup for flat artwork is two matched lights placed symmetrically at about 45° to the artwork. That gives even illumination and works well for many pieces.

The best setup depends on the artwork:

• If texture matters and you want brushstrokes or surface relief to show, use more oblique light and a relatively harder source.
• If you want to minimize texture and reproduce the work as flat and even as possible, use more frontal, diffused lighting.
• If the surface is shiny, glare control becomes important and techniques similar to photographing work behind glass may help.

You do not necessarily need expensive studio strobes. For smaller artwork, two off-camera flash units/speedlights can be enough. If the camera is on a tripod, continuous lamps can also work with longer exposures. Avoid fluorescent bulbs because they can cause poor color reproduction.

Useful basics: tripod, two matching lights, two light stands, simple remote triggering if using flash, and possibly diffusers/modifiers. A color checker chart is also a good idea for accurate color.

For focus, yes—room lights can be on to help focusing, as long as they don’t significantly affect the exposure. Stopping the lens down to around f/5.6 can also improve sharpness.