Familiarize yourself with local laws and folkways. A good idea is to find online resources in your language that are written by people like you who did it before you. Expat.com, the expatriate community is a good place to find blogs by people who did it.
Learn a modicum of the local language. I've found that I had good results going through the first (A-level) course on Babbel, your mileage may vary and you might find Rosetta Stone or Lingua easier.
Get a hand on local insurances your employer doesn't provide. In some European countries, for example, it's a good idea to have an indemnity insurance. In the United States you might want to spring for an additional health insurance package.
Set up two drop box accounts, one in your home town, one where you're moving. That way you can receive mail on both ends at all times. Switch your home address over to the drop box account (I use one with forwarding with US Global Mail, they scan and/or forward mail they receive).
Send yourself, to your new location drop box, a bunch of things you'll have to find in the new place. Like, you know, contact lenses with your prescription. Or one or two computer keyboards with your key placement. Trying to get, for example, a US layout keyboard in France is almost impossible, and asking for it might get you snarled at. Enjoy your AZERTY.
Create two folders, one to leave behind and one to take with, both containing all important information about your home country accounts and other things. Hand the "home" one to someone you trust. Get that person power of attorney and access to your bank accounts, etc. These days you can even do this online on a Dropbox, OneDrive, or Google Drive account.
Set up and arrange means to communicate with people at home. Get your family familiar with Skype or Hangouts or Facebook Video Chat or whatever. WhatsApp won't work as well, since you'll have a new number. Choose a service that isn't dependent on your phone number, having a phone (something that works on computers, tablets, and phones), and OS.
I missed many things, I am sure. Hope the comments will add to that :)
Images were taken by me at the Strand Promenade in Scheveningen. They're part of the SprookjesBelden exhibit, "fairy tale statues."