Leaving a scripted voicemail can improve lead response rates anywhere from 3% to 22%. 70% of local searches online result in a phone call; In 2014, 80% of callers sent to voicemail said they do not leave messages because they don’t think they’ll even be heard.
After each one, evaluate your performance. Most systems provide the option of listening to the message you just left. Doing this as much as possible will improve your performance more than anything else. Would you save that voicemail? Would you return that call? Would you return that call right away? Are you missing the basics (alternative phone number, optimal ways to get in touch, a fall-back person to call)? Did you craft it or wing it?

Website: https://support.8x8.com/express/devices/voip-phones-headsets/8x8-express-how-to-create-or-change-outgoing-voicemail-message
Arguably the most intimidating factor when leaving a voice mail is the fact that once you leave the message, "in one take," there is no taking it back. That is why, especially in the business world, an overwhelming amount of people revert to email rather than leaving a voice mail message. Especially in a technologically advanced world, email or text messages are now used as a primary form of communication. Although there is a good argument behind opting for the written word over the spoken one, an email can lack the human touch, the emotion and enthusiasm in a voice, that can often times generate a better response. In fact, there is no impact that compares to delivering a clear, concise, professional message through your own unique human voice.