This might seem obvious, but make sure you clearly state and restate the dates you’ll be out of the office. Even if you put the dates in your subject line, you should also repeat them in the message body. It’s hard to over-communicate here. State exactly when you’ll be back, and whether or not you’ll be responding to calls and emails while you’re out. If you’re on the road but are responding to messages, let everyone know if you’ll be unavailable for an extended period (while on a flight, for example), if you’ll be in a different time zone, and in general, that they should expect a delay in response time. All in all, set realistic expectations and strive to be as specific as possible.
Additionally, you can reference a person in charge of your business while you are way:

I take advantage of the ability to send different OOO messages to internal or external addresses. Internal addresses get a couple of people to contact if it’s urgent, usually my direct report and my backup person, since between them they can cover pretty much everything I do, or at least they’ll know who can. External addresses get a more general notice: “I am temporarily out of the office. If your message is regarding the Llama Care project and requires a prompt response from our Llama Grooming Team, please make sure that [email protected] is one of the recipients of your message.” Probably not the most elegant phrasing, but we have a distribution list for this very reason. Even requests that they know only I handle are supposed to go to the LG list.
9. Auto Reply Example with Alternative Contact Phone and Email. [Your Greeting] Thank you for your email. Unfortunately, I am out of the office until (Return Date).