You're moving to another country. You have the next step in your career ladder and you are going for it. Some day you know you will return. Which of your relationships matters so much, that you want the relationship undamaged when you return? These relationships will change but you want to ensure that they are undamaged. If you meet with someone at least once a week, then they may find someone else to meet with on that day at that time, so when you return things will be different.
Take steps now to tell everyone who is important to you about the move, especially if they are in the same company as you. They will hear it on the grapevine and that will tarnish the relationship at least in the short term.
Consider time zones and when is the best time to catch up with people.Getting computer software like Skype and a webcam, which will ensure you can see each other will make a tremendous difference to your relationships. Unfortunately it means you cannot phone someone just after a bath or a bad hair day but it will all take planning.
Remember birthdays. The grandparents may not see your children every year; this is a good time to make sure you send those photographs and cards. Get a height chart that you can include in the photo, that way they can see how much the grandchildren have grown. The same goes the other way that you need to remember the birthdays of the grandparents. One major factor could be the speed of postal services, especially of someone has a birthday near Christmas the postal delays can be excessive and need to be planned for.
What about friends? What do you talk about? Do you share hobbies, sport, or church? Get them to keep you in contact with what is going on among your friends and acquaintances so that you are up-to-date.
A newsletter is a must when you have a large circle of friends and you may need to continue it when you return, for those you meet in your new country, but the chief relationships need a much more personal contact (a handwritten letter is worth far more than one typed on the office computer).
If you are going to have time to visit your home for a short period then you will almost plan it like a military operation to see your chief friends and family and as many of the others you can fit in. However well you plan you will find that some might be offended because you didn't spend enough time with them. It is part of living in another country, and when you do return to your home you'll find your time is limited.
