The main title in "A fistful of dollars" is legit my favourite one of the trilogy. I like it maybe even more than "the good, the bad and the ugly" score. It's just... So simple and one of the greatest testaments of Ennio Morricone's génius ever displayed.
One of my favourite things about it is the simplicity. It uses just things that people would have available in the wild west, which I feel makes the real difference in building the atmosphere.
The wind – obviously you cannot use as an instrument, so, to imitate the howling of the wind over the wide, bare dessert, he uses violin (and later other string instruments)
Whistling – which, obviously, cowboys were able to do
Bells ringing – like the ones in a church, the clinking also reminds me of spurs (obviously you can't use spurs as an instruments, so something that's also shiny, clinking and metal comes to play – the bells)
Whips cracking – which, many people had to have whips on the wild west
Male chorus – [see whistling above]
Acoustic guitar – is there to essentially string (ha) the melody together. Pretty much the only instrument used that doesn't symbolise something else, and thus the music theme is built around it.
[in a few parts of the soundtrack, instead of acoustic guitar is used the electric one = I love Ennio Morricone so much :D]