Use the general keys in a (local) fern (Pteridophyte) flora. There are several for India. Otherwise use the followong elink to FOC: http://efloras.org/florataxon.aspx?flora_id=2&taxon_id=51
In the case of Indian fern scenario, there are fern floras for the Himalayas, central India and Western Ghats along with many other literatures including monographs of various genera/species which can be useful for identification. Also refer to the following link for more information and pictorial guidance to ferns and fern-allies:
The main character of Pteridophyte is availability of spora, so firstly you can see the location of sorus. The location is different for different genus. and then you can differenciate another characteristic of spora (colour, size, availability of inducia, etc). You can see many books for references like Fern of Malaysia in Colour (Piggott 1988).