Like Peter says, the light needs to come from the sides so that the reflection does not go into the camera. This is what I do when I photograph my sketches. Scanners can be problematic, which is why I photograph my work. I also follow Peter's suggestion of masking out problematic lights. Glare coming off a piece can be tricky to control and it takes a bit of time to figureout the problems. Overhead lights can be a bugger as they are reflected off many surfaces and spot reflections can create problems.
Polarizing filter will only help if you are using polarized light, otherwise it is a waste of effort.
Tripod does help, especially when you try to standardize your photographic process to make it efficient and constant. I use a rig that always holds my work in the same place and position , no matter its size, and the tripod takes away any issues with the camera, such as fiddling with settings and aiming.
Just some ideas
Alex.