hmmm... the way i identify :
wht ever has an adjective : nela kamal -> karam darya samas
wht ever comes like : mata- pita -> dav dav samas
wht ever is like numbers : trilok -> dvigu samas
things like pratyek and stuffs -> avyavibhav samas
things related to god : nerkant -> bahuvirihu (note : it can also be put in dvigu samas so both is right)
the rest all which u feel as u can add "ka, ki, sa, me, par, ke liye, ko, ke," -> tatpurush samas
hope this helps... like pls.. ^_^