Users often don’t invest enough time into their messages, resulting in incomplete, unprofessional, or otherwise under-whelming greetings. Sure, crafting a greeting doesn’t sound all that complicated; however, there are a number of pitfalls users can fall into—i.e. informality, terseness, sincerity, lack of direction, and more. While none of these sound too catastrophic, they are often interrelated. As such, they tend to worsen any problem. For example, humor can cause informality, worsen ambiguity, and weaken sincerity. That being said, users should strive to avoid ALL these pitfalls.
If you are going to be unavailable for a predetermined time, let people know. Example, if you are on vacation for the next two weeks, inform your callers in your greeting that you will be returning calls on such and such date. This way they expect it to take a couple of weeks before you get back to them instead of stewing over why you haven't returned their call.

Voicemail plays an essential role in business operations. It captures all the missed communications from your customers so your employees and departments can respond to them quickly.
Rehearse or write down your message before recording it. Remember that old saying “practice makes perfect?” It’s certainly true when it comes to creating an electronic greeting. The more you’ve rehearsed, the easier the message will be to restate. If you don’t have time to practice, writing down the greeting before recording it – and then reading it aloud from the paper – may help you stay focused on the correct wording.