Museum Gallery Photography: The Room Is the Picture, Not the Painting
Almost every photograph taken in an art museum is a bad copy of something that already exists in better quality on the institution's own website. Point the camera straight at a canvas and you get a slightly crooked, slightly reflective, slightly warm version of a picture anyone can look up in thirty seconds. The interesting photograph is the room the work lives in and the people standing in front of it.

Here there are three layers. Bronze heads in the near foreground, visitors in the middle standing with their phones up, and the big Matisse on the far wall carrying the colour. Remove any one of those and the frame collapses into a snapshot of a wall.
Shoot from a corner, wide, with something close
Stand in a corner so two walls recede away from you at an angle. Put a plinth, a bench or a doorway into the bottom of the frame at 24mm or 28mm equivalent. That near object is what gives the gallery its depth, because galleries are designed to be visually empty and an empty white box photographs like nothing at all.
Keep the verticals straight. A gallery is a box of perfectly true lines, so any tilt reads as a mistake rather than a choice. Straighten in camera if you can, since correcting later costs you the edges of the frame.
The lighting is aimed at the walls, not at you
Track spots are pointed at the artwork. The middle of the room, where the people are, sits two or three stops darker. Meter for the wall and the visitors go to near silhouette, which is usually the better picture. Meter for the visitors and the painting blows out and stops being the anchor.
Expect ISO 1600 to 6400 and shutter speeds around 1/60. No flash, no tripod, and in a fair number of rooms no photography at all, so read the wall placards before you lift the camera.
White balance is a decision, not a correction
Halogen and warm LED on white walls will fool auto white balance into rendering everything cream. Neutralise it and the room turns clinical, which is honest but cold. Leave a little warmth in and it looks like the place you actually stood in. Pick one deliberately instead of accepting whatever the camera guesses.
For glazed works, come in thirty to forty degrees off axis. You will lose the geometry of the frame but kill the reflection of your own shirt.
Photograph the people photographing
Someone crouching with a phone raised at a canvas is the most honest thing happening in the room. Backs of heads, arms up, screens glowing with a small duplicate of the artwork. That is a picture about looking, and it belongs to you rather than to the museum's image library.
The wall label is not the subject.