Nifty on weekly charts nearing an important support trend line which should be around 10830-10800. 10856 is 50% retracment of total rise 9951 to 11760. Below 10850 we can see another 100-200 points, 10642 is 61.8% retracment of that move.

So buying can be start here. 

Disclosure: I am not a SEBI certified analyst and this is not a buy/sell call.