Taking a good picture of your rig is not as easy as it looks. Most of the time, rigs are made out of of the least photographic components of all: stainless steel / aluminum. Being highly reflective, these material make it super easy to blow the highlights.
To make matter worst, the other parts are often black so trying to protect the metallic highlights by under exposing will remove all details from the black parts. What a challenge!
The solution is to shoot in an environment with a good ambient light level and no hot spot. The easiest way to achieve this is to use a [light tent], which has the side benefit of also removing reflections.
If you dont have a light tent, you can use a huge softboxes or point your flash to a white ceiling/wall to turn it into a big light source. The important thing to keep in mind is to make the light as big as possible and to have it wrap around the subject.
The next challenge is to figure out how to hold the rig while taking the picture. While this is not an issue for tripod mounted rigs, it is a completed different story when the rig cant stand by itself.
In my case, I used my trust worthy Manfrotto Magic Arm to hold the rig in the correct angle. Another solution is to take a picture of yourself holding the rig, or better yet, ask a cute girl to do it for you.
What kind of background should you use? White, Black? Pick which ever you want and do not be afraid to use non standard colors too! Just aim for something as uniform as possible with no distracting details.
Do some adjustment in Photoshop, but no need to spend too much time cleaning up the dust and cats hair on the rig, the picture will not be big enough for others to notice. There you go! Create your rig profile and you are set.
Here is the before/after picture of my Sumo rig. As you can see, the original is far from the end result. I planned to use two strobe but ended up using a single one because I could not find my extra batteries. This resulted in a very uneven illumination. Still, it took me less than 5 minutes to clean up the image. I used mostly the Quick Selection tool in Photoshop to remove the background then fixed the exposure with a level curve.