Try to avoid unnecessary phrases that only make your greeting longer, like “leave your name and number and what you’re calling about.” Most people know what “leave a message” means.
When someone dials a new number, they may consider if they have got it wrong, especially when it rings through and reaches voicemail.

Leave out excuses like “I’m probably with a client right now” or “I’m unable to answer the phone right now” – it’s obvious you can’t answer your phone if a caller is listening to your voicemail greeting!
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.