Instead of stating the obvious, enhance your message with information your callers can use, such as how to reach someone immediately, when you will be returning calls, or where they can obtain after-hours service. Services that offer multiple custom greetings like Tendant allow you to store multiple greetings so you can have a greeting just for a holiday that you can use every year. Specify the information you want callers to leave. Your voicemail greeting presents a great opportunity to gather important details that will help you better serve your customers. This may include account numbers best times to return the call, and of course, a brief summary of the issue or purpose of the call.
For one, be sure to understand QoS (mentioned above). This means going beyond understanding the concept and moving to how the networking equipment in your office -- or your employees' home offices if you're still at that stage -- can actually implement QoS. Most business-grade networking hardware will be able to handle QoS in more than one way, so testing which method will handle voice traffic more smoothly in your environment is important.

Likewise, voicemail can gain some power here. Users can listen to their messages online, download messages to offline storage, and manage notifications by listing an email address.
If your customers feel that you don’t care, they’ll take their business elsewhere. Experiences are the differentiating factor between businesses. Big efforts to improve the overall experience in tiny ways by crafting a voicemail greeting script can make a huge difference when customers are asked by their friends and family how easy it was to work with you. And word spreads quickly in the age of social media. The more positive experiences you offer, even when you’re not available, the more likely those people will call back.