First, try to use some watered down soapy water to see if that helps clean it. If that doesn’t work well enough, I have found that basic Windex without ammonia (I repeat, WITHOUT ammonia) does a pretty good job of cleaning up dirty buttons and knobs. Even when it’s been watered down to 50% strength, it still does the trick in most cases. And try using a Q-tip with the Windex when cleaning. Afterwards, rinse the surface with a bit of clean water added to a clean clothe or Q-tip (and not to the surface itself), and then pat dry with another clothe (preferably lint free).
NOTE: Test the surface first to see if anything gets rubbed off when using a cleaner. I say this, because some off brand ammonia free cleaners could still have ingredients in them that may damage the surface you want to clean.