BE SURE - Moving can be extremely stressful, be as certain as you can be that it's right move for you before you go. If possible visit country before you make up your mind, don't rely on other people's impressions. Ask yourself if new culture will really suit you (and your family).
BE PREPARED - ...For anything and everything to go wrong. Don't assume that you'll be able to find perfect job or house immediately. If possible make sure you've got enough money to see you through first couple of months at very least (preferably longer). And to do that you'll need to...
BUDGET - As unglamorous as it sounds, good budgeting could be what makes difference between a successful relocation and a disaster. Before you go, work out what everything is going to cost during those crucial first months when you're trying to find your feet in a foreign land.
DON'T DELAY - Start preparing as early as possible, just getting all necessary paperwork in order can take a long time. Make a checklist of everything you need to do!
CHECK YOUR BENEFITS - If your company has initiated your move you may be eligible for relocation benefits. Make sure you ask if they haven't told you already!
HEALTH - Make sure that country you are moving to has adequate healthcare facilities and infrastructure to support you (and your family), especially if you suffer from a medical condition which requires treatment or medication.
YOUR HOME - Think about what you want to do with your current home (e.g. sell it, lease it, leave it empty) and what kind of accommodation will be most suitable in your new country. If you don't know anyone in new country who can help find accommodation, consider services of a relocation agent.
EMPLOYMENT - Will you be looking for work in your new country? If so, consider starting your job hunt before you go (use Internet!) Will you be able to use your existing qualifications or will a period of retraining be necessary? If you're moving somewhere where they don't speak same language as you then you should...
LEARN THE LANGUAGE - Few skills will have such a positive impact on your relocation experience as being able to speak, or at least understand, local language. Getting to grips with local lingo before you go is a great idea!
PAPERWORK - No matter how insignificant that old document at back of bottom drawer may seem now, take it with you, chances are at some stage you'll have to show it to someone. Moving countries can be a bureaucratic nightmare at best of times but if you come prepared with necessary paperwork you stand best chance of a stress free relocation. Things to think about include birth certificates, wedding certificates, educational certificates, medical certificates (including those for your pets!), etc.
FRIENDS & FAMILY - Don't forget to inform everyone of your new address and when you're going (unless you don't want them to find you, of course ;-) Seriously though, saying goodbye to friends and family can be hardest thing about leaving, be prepared for an emotional rollercoaster ride as day of departure draws near.