plant cemetery

oh dear. we've killed another plant!

i really don't know what it is that i do wrong but every plant i have ever owned has died.  even the basil plant died!
what is it that makes some people really green fingered and some people plant killers?!
i think i must take after my mum. when my brother and i were younger we never really had any plants at home as i remember my mum saying one day that it was cruel (she always killed them too!).
maybe plastic ones are the way to go....?!