What an interesting thread! During the 60s I found myself adopting a singing 'style' that only seemed to exist inside folk-clubs (a bizarre sound!). Then I remembered my grandad singing simply for his own enjoyment (his favourites were 'the wee cooper o Fife' and 'the muckin o Geordie's byre') and I've spent the last 40+ years trying to take his simple approach (he died when I was 12 years old!!). I was also lucky to hear Jeannie Robertson, Belle Stewart, Jimmy McBeath and Davie Stewart (although I didn't fully appreciate them at the time - which explains my attempts at the bizarre style).
So I echo what's already been said - just sing with you own voice (but, as Cap'n Birdseye says - listen to some good old ones as well).