1,- Go to local English corners
2.- Participate in a few Forums, plenty around.
3.- Do a screening, when you feel comfortable, contact one por more privately for a beer or a coffee somewhere, and start a friendship.

But be aware and do not get upset, many Ex-Pats are afraid to meet others because they do not wish to hear money petitions.

Good luck.

forget english corners, its for chinese students!!
got to nightclubs, bars, coffee shops, and restaurants where you enjoy foreign imported food and drinks..
The best way is to meet expats are at the cheap hostels in beijing and shanghai, many travellers also spend their night there...
I spent 2 weeks in Emperor hostel in Beijing, in that alley where the hostel is, you meet so many people and there are many hostels there with bars and restaurants, people were so friendly there.. 

But this begs a broader question -- why come to China to meet expats?  I came to China to meet the Chinese.  If I had wanted to meet expats, I would have stayed at home, leading a moderately comfortable moderately middle class life.  Additionally, for whatever reason, I have often found that a good number of the expats that I have come across in  China are not exactly the sort of persons that I would have ever invited to my home for dinner.  

It's actually pretty easy to meet other expats in Shanghai.  Here are a few tips:

A lot of expats tend to hang out in bars or pubs.  Start checking them out, especially ones that serve western food.  Sooner or later, an expat is going to be screaming for a burger and they will go to one of these places.  Plus, it's nice to meet up with some people and speak your native language in a comfortable setting.  Dance clubs are NOT good for this.

There are many expat websites that focus on Shanghai and have listings of popular restaurants and pubs frequented by foreigners.  Check here on eChinacities under shanghai - either nightlife or clubs and bars.  Other good ones are cityweekend and That's Shanghai!  The latter 2 also provide free monthly magazines that can be picked up all over the city.  They will give listings of places and even events that expats might enjoy (and it's all in English).

If you are looking for a place to start, head up towards Hongmei Lu in the Gubei area of Shanghai (sort of north-west part of the city).  There is an alley there called Laowai Jie which is full of foriegn owned restaurants, pubs, breweries, bars, and things like that.  TONS of foreigners go there.

Lastly, when you find some, just be friendly and strike up a conversation.  I've met most of the people I know just by going out by myself and saying "Hey, how are you doing?  Where you from?"

Good luck!  It's not very difficult to do in Shanghai!

Meeting other foreigner in Shanghai or other cities is fairly easy:

1. get QQ international messenger and start joining all the chat groups related to foreigners living in China

2. visit places like Starbucks, KFC, McDonalds or pizza hut where foreigners seem to hang out.. It is bold way of meeting people but you would be very surprised how many people will actually talk if you start the conversation

3. go out to bars in the evening, where foreigners seems to visit but not one of those loud bars where no one can hear anyone talk but the small type. In Shanghai, there are a lot around that doesn't have loud annoying music blasting in your ears.

4. if you work for a company that employees foreigners, get to know them and their foreign friends. Other than meeting new people, you are also networking, which can benefit your career

5. Use any opportunity you can, talk to foreigners when you are grocery shopping, out for dinner or standing around looking for a taxi. Start off will a little small talk, it might lead to bigger conversations.

The biggest secrete, speak out and don't be afraid to talk to people. I have met a lot of people here, both foreign and Chinese.

go to night clubs and bars and you will find bunch of foreigners there