Here are some things I have done in preparation.
- Call them to see if they have questions beforehand - this will introduce you to them a bit and help them feel more confident
- Arrange for a coworker to introduce them to the rest of the team and give them a tour
- Set up a video conference with them ASAP on their first day - since you can't be there in person, this will break the ice and help them put a face to you.
- Ensure their office environment and equipment is available
- Ensure onboarding info is up to date
- Plan a trip to the office soon if possible to meet them in person. This speeds up relationship building and camaraderie.
Edit based on comments and experience: It is highly preferred to be there on their first day. Otherwise you have to rely on your teammates for a lot of work like ensuring their desks are set up, and helping with computer log on before they have access to their phones/video conferencing.
You should also do the basics you would with any new employee: clarify expectations on work hours, communication, and individual contributions.