I've tried everything and I'm still getting 80+% failure with these things.

I've followed a few website's advice, some say use hormone powder, some say
don't bother, I've not bothered.

I've been taking a 3-4 inch cutting from just below two leaves and removing
any flower buds, I've been taking off surplus leaves leaving just two plus
the growing tip.
I've tried getting them to root in water, but frankly two months is too long
i think, and this is before even very short fine roots appear, but even then
once they go into compost, they're shrivelled up within days.

I /may/ have been sucessful, although it's still early, but some I took a
fortnight ago and just shoved them into a pot containing ferns (very shady
area) seem to be holding up OK.

I've tried various light levels from full sun to full shade and not really
noticed any difference.
I've tried them with and without clear bags (for humidity) and this hasn't
made much difference neither.

Do they have a preference with regards to compost? - I've tried three
different brands and not noticed that any is better than another.

Is fertilizer a good or bad thing?

Is it the wrong time of year? - I thought if I took them late, they wouldn't
have time to root before winter.