Using the gear you currently have.
Step the furthest away you can. Normally on the other side of the room.
Then choose your focal length for that distance. Depending on the room, and the area you need to cover of course. Stepping away will force you to use the longest focal length you can. Avoid wide angle lensesAvoid wide angle lenses (a).
If you really have plenty of room, for example on a gallery you probably can define first your focal length (if you have for example a prime lens of 85 mm, then step back until you have the frame you want.
Use a firm tripod (a shaky tripod is not useful), point the camera exactly perpendicular to the center of the wall, and at the middle point of the area you want to frame. Do not tilt, do not pan.
Use the sweet spot of the aperture of your lens (as Alan Marcus pointed) probably f8.
Define your aperture and ISO depending on your camera. An ISO of 200 is fine.
Turn off any "Anti-shake" of your lens.
Use a remote shutter trigger, or if you do not have it, use a timer on your camera, of at least 3 seconds so you are not touching the camera when it fires.
If the room you are in has too little light you probably need to use some flashes, bounced around (depending on a lot of variables) so you reduce your shutter speed and avoid noise.
(a) If the target wall is too big, and you do not have much room to step back, probably you need to compose several shots.
There is a chance you still need to correct some stuff on the image, eliminating some distortion of the lens.
Some of this can be corrected using your brand's software, or you can use DxO that has signatures of lens-camera combinations to correct some of the intrinsic problems of them.
All this without thinking about lighting, white balance or noise.
If you still do not get good enough results, you probably need to rent some better gear.