How to Meet Other Expats

Moving to a completely different country can be stressful. Having a support group can greatly help you out. If you're in a popular country, like Italy or China, you can probably throw a stone and hit a foreigner.However, if you're in a less popular country, then you're going to have to make an effort to meet foreigners. You might also want to take a look at 30 days to move abroad. It makes moving overseas a breeze.
Before You Go
Your local college or university might have international students that you can get in touch with before you move abroad. They can answer some of your questions about living in their country. They might also be able to put you in touch with family and friends still living there.
Online
Things are a heck of a lot easier than they were years ago. With the internet you're never truly alone. You can easily email, chat, or even call friends and family back home for free. Even the most backwater towns seem to have internet. Some sites are blocked in countries such as Saudi Arabia and China, but proxies, such as hidemyass will get you around firewalls.
One of the best ways to connect with teachers in your area is the internet. Dave's ESL Cafe is a great place to start. They can also tell you about other forums, such as waygook in Korea. Facebook is also great. You can create groups and plan events. Word spreads fast among foreigners. Another good place to look for foreigners is meetup. You can search by area as well as interest. Twitter is also a good place to try to meet foreigners in your area. Don't forget about couchsurfing. You can meet foreigners and locals alike this way.
Meeting People Locally
If you're going to take a TEFL certification course in the country where you're planning on moving to, that's another good way to meet foreigners. You can even exchange job tips.
Your school is another place, especially if you're in a small town. Sometimes the people at your school may be the only foreigners in the whole town. Like kids who become friends quickly, people working abroad also quickly form friendships.
Some teachers will be the only foreigner at their school and if this happens to you don't worry you'll still easily to meet other foreigners. We tend to stick out like sore thumbs. There is usually a foreigner bar or two in your town, so you might want to try that. Churches are another place where foreigners gather. English book stores as well as foreign restaurants and grocery stores are worth checking out.
Events
The British embassies and the Canadian embassies have a bar and the Irish embassy is usually very helpful due to the fact that there aren't that many Irish abroad as other nationalities. If you're American, you're pretty much screwed as far as embassies go. The lesson? Befriend a Brit or Canuk so that you can get into the embassy bar.
Try to attend a conference or two. You can meet new  people, learn the latest about TEFL, and network your way to a better job. Ditto goes for joining the local professional TEFL organisation, such as JALT in Japan or KOTESOL in Korea. Check IATEFL for a complete list. Big language institutes, such as EF, Berlitz, IH, and the British Council might host events or training sessions for foreigners.
Organisations
If you've worked with the Peace Corps, VSO, or a similar organisation, you might be able to use their returned volunteer services and contact current or former volunteers that are still living in that country. Military organisation, such as the army, marines, etc, may also help out former servicepeople.