Q: I have an imac in the office and a macbook air at home. What is the best way to share files between the two computers?

What quantity and size of files are you talking about? There is i-Cloud, email, memory sticks, CDs, portable hard disks and so on.

"Best" can be pretty subjective but the following are a few of the options that you may want to explore:

iCloud Drive:

http://www.apple.com/icloud/icloud-drive/

iCloud Drive FAQ - Apple Support

Dropbox: https://www.dropbox.com/

If you are using Microsoft Office: https://onedrive.live.com/about/en-us/