I may be wrong, but I am pretty-sure their office front door is a good place to start

Through the roof! Mission impossible style.

Goodluck

Produce better work than the thousands of other highly talented architects trying to get their foot in their door. xD

If you're living in the UK with a visa - pretty easy if your good as they hire boat loads all the time - but if in India, looking to get sponsored, pretty hard - no chance as there as so many archs in the uk already.  UK gov has tightened up visas -

Unless fosters is doing a project in India not certain you stand a chance.  

Better off if you're qualified, come to the UK and do a 1 year MA.  And then knock very hard and continuously on the door. 

And foster's projects are so generically banal and corporate, you should really set you bar a bit higher, mate.

Apply, interview, work.

They have like 2k employees, it can't be that hard to get a job there.

 

Give them a project

Is this a trick question? Apply like anywhere else. Except for certain direct recruitment happening out of whatever school one of the practice principals may be teaching at the moment, there's no secret recipe to getting a job at one of the "big" names, like F+P. You apply. If your experience and salary fit what is needed at the moment you will get a job. If you enjoy the starchitect vibe around you and you don't screw up badly, you will stay. Possibly you will even have a career of sorts. Otherwise you will do what so many others have done and work there for a couple of years and then move on. Simple as that.

why the hell would you want to do that

Its very telling how many people are critical of your desire to even try to get a job with them.  There are thousands of other firms that produce just as sterile corporate work, and you wont have to race against thousands to get a job with them.

I got through the intern criteria ,but they  take there interns from November,Now  iam placed in India only for sometime