A good voicemail greeting is short and professional, lets people know that you’ll get back to them, and invites callers to continue engaging with a call-to-action. You should also show your personality if you’re in an industry or role that allows that. If your industry is more conservative, however, you’ll want to keep humor and personal touches to a minimum. A greeting Your name Your company A simple explanation for missing the call (e.g. you’re away from the phone or are on holiday) A rough estimate of when you’ll get back to the person An alternative person to reach out to (if you’re out of office) An alternative mode of communication (if you prefer email or text) A call-to-action such as “Leave a message” or “Send me an email at [email protected]”
I've stressed it throughout this article, and I'll stress it again — your sales voicemails have to be concise and airtight. That requires being locked in on exactly what you're trying to get across. You can't go off on a series of tangents that may or may not apply to your prospect's situation. Keep your messaging as focused as possible.

This script comes from Donato Diorio and it's quite simple and to the point. But it still does a great job of highlighting prospect benefits and the follow-up plan.
And also don’t forget to write down your message just in case you get too anxious and forget to say your name at the end of the message.