A properly treated corset...

...will not have to be cleaned very often. When it has to, it is necessary to remove the metal boning and then dry clean it, unless it is marked that the stays will not rust, but in general the firmness and smoothness may be adversely affected by the cleaning processes, and especially for highly stressed corsets that are used for figure training this reduces the garment's structural integrity. Always inspect your corset for damage. If you catch it early it's usually easily repaired. Common areas for damage are the eyelets in the back, ripping out due to incorrect lacing, e.g. not enough pulling of the lace crosses and too much pulling just at the waist. The other is usually from long term wear with steels poking through at the edges. The corset stretches in circumference and as a consequence it gets shorter top to bottom to compensate. Spiral stays are less of an issue, but solid steel stays cannot compress, so they eventually wear through the edges. Good corset designs accommodate this with a variety of techniques, but even then,  wear over time at the edges is significant. Lastly, older corsets, or those that have been cleaned too often, may have thread wear at the seams, causing ripping at the seams. This tends to be an overall structural weakening and the corset is likely approaching the end of it's useful life. If you do have an older vintage corset, I suggest you preserve it and study it's construction. If you plan to tight-lace, you really should get a modern and new corset. For example Melanie Talkington from Lace Embrace, has mastered the art of classic corset making and authentic reproduction.