There are issues you have to make sure they are in order. I have written down a list of such things:

Proper and valid visas & passports

These are the most important single issues affecting your entry to the target country. If you don't have appropriate visa in order you simply will not be permitted to enter the country if it requires visa. Also, there usually are rules that your passport must be valid at least 6 months after your entry. As the assignments sometimes get extended and you might want to travel around a bit as well, it makes sense to apply for a fresh and long lasting passport before you leave from your home country. Also, if your passport expires during your stay you have to apply for new passport and then apply for new visa, as the visa is actually a stamp in your active passport. Some countries also offer e-visas for certain nationalities, but vast majority of visas are still traditional "hard and tangible" ones.

Usually your company will apply for the visa for you and your accompanying family members, as they need their own visas as well. Also notice, that you are not allowed to work while holding only tourist visa. For example, China used to be quite flexible when granting working visas for foreigners, but recently the rules have been tightened noticeably and visa classes have been revised. There have been stories about foreign individuals who have been living and working in China for years on short-term visas and frequently refreshing the visas, but their applications have been denied recently. Just to demonstrate how easily regulations can change.

Find out where you pay taxes

In some cases where you are an sent employee, you will be kept on your country of origin's payroll so that your salary will be paid there, while in some cases your salary will be paid to your destination country. This might seem trivial as salary is always salary, but in fact where it gets paid affects multiple things. Firstly, the country where your salary is paid will tax your income according to its taxation regulations. Which country has lower taxes is simple to check and if you feel you would like to be paid directly to your destinaiton country, its always worth it to ask for it. In some cases the issue can be negotiated between the sending company and the employee, while laws might force you to accept either way. It really depends on the case.

The coin always has two sides though. Your total purchasing power depends on exchange rates if your country of origin uses different currency than your destination. Countries with strong and stable currency history are usually favorable when making the decision when compared to freely floating currencies, but things might fluctuate in unexpected manner. For example, during the current economic crisis the purchasing power for expatriates has been changing quite a lot globally, as central banks have been trying to maintain the value of their own currency. For Europeans and especially for euro-currency the purchasing power in Australia has been changing a lot during the last year due to depreciation and appreciation of Australian dollar. The same has been happening in larger scale here in China due to strong Chinese Renminbi. If your salary would be paid in Chinese currency the current exchange rate would be favorable to you and you would get more bang for your buck in Europe. Whereas if the salary would be paid to an European account, your status compared to other Europeans would be unchanged due to fact that Euro is the de-facto currency in Europe.

Banking issues

Find out what kind of arrangements are needed for you to be able to manage your daily life moneywise. Credit cards are great but they are not accepted everywhere, especially rural areas tend to have less coverage for acceptance. Cash is accepted everywhere so you have to have a reasonable access to that as well. Credit cards help with this issue as well but there really is no point to pay withdrawal fee for the CC-company in question every single time you need some cash. If possible, it makes sense to create a local bank account and get an ATM-card for local payments and withdrawals.

A word of warning though, if you are relocating to a country whose language you are not conversant with (like China), make sure you will have local help available to translate everything. For us, all the documents needed were in Chinese...

Insurances and medical issues

As you are relocating to a different country, your employer will most likely acquire comprehensive insurance package for you and your family just to make sure you will get at least as good medical care as you would at your home country. If this is not the case, demand such insurance to be included in your package as healthcare even in trivial cases can be extremely expensive. If possible, investigate beforehand where and what kind of medical centers are meant for you to use, and if this is not possible do it immediately after you arrive.

Vaccinations might be required in some parts of the world so doublecheck your own and your family's status. Even if your actual place of stay does not actually require you to take any exotic vaccinations, a good way to prevent possible problems is to keep at least your basic vaccinations like hepatitis A and B up-to-date. But usually starting expatriate life means that you'll end up traveling a lot more than you used to, partly to get away of it all and partly to exploit the situation and explore countries that are close by. Remember, traveling around will give experiences you just cannot buy with money.

Change your address details to the relevant parties

Notify all the parties who need to know that you are relocating and if you want to keep on receiving mail from them, be sure to provide your new address details. Also things you consider you do not need any more, can be simply terminated. These may include cable tv, internet connections and newspapers.

Property and belongings at home

This is a bit more complicated issue and deserves careful and thorough planning. What will you do with your propesty that has to be left behind unused? Will you sell it, rent it or just let it be as is? There are different aspects affecting the decision, for example the length of the work assignment overseas, the type of the property (apartment, car etc.), expected change in value, overall financial situation, plan to come back or relocate totally, how easily the asset is to replace just to name a few and not to even mention personal ones. Many expatriats choose to sell their existing car before leaving as it is bound to lose a lot of its value unless it is something even remotely unique. If your assignment is long enough and your home country's tax laws allow, you can perhaps buy new one from your destination country and bring it tax free back to your home country.

There are as many correct answers to this issue as there are expatriates to be. The best advice is to think everything thorough well in advance and make the decision based on facts.