For example, this is how Nextiva’s call analytics page looks like. You would need to track how many users hear each voicemail greeting and how they responded. Voicemail greetings with a higher score of customers leaving a message are working efficiently. Voicemail messages that are not even heard completely are a failure.
If anything big changes- address, phone, etc.- make sure you correct your voicemail early on. Keep It Short; We know, we know. We just gave you all this information and we’re now telling you to ‘keep it short‘. But, a professional voicemail greeting (or any for that matter) shouldn’t go beyond 20-25 seconds.

“Hey there! This is [name] at [XYZ company]. Thank you for calling. I can’t take your call right now but if you leave your name, contact info and reason for calling, I’ll call you back right away. Take care and speak with you soon!”
Do they want to sit through an IVR menu that may or may not direct them to the right person? Do they know you’re a one-man/woman team and there’s no reason to sit through a menu? Skip the menu entirely and let them leave a message as quickly as possible. There’s no reason to add any additional steps or make your customers go through leaps and hurdles to leave a simple voicemail. When you identify what your customers’ pain points are, you make it much easier to determine what you want them to do to save everyone from the unnecessary stress.