Kev, an old one or a new one? I have messed with several old Vaqueros and Blackhawks (and Security Sixes and Redhawks and Super Redhawks), and was all set to do my usual Ruger thing when I got a pair of New Vaquero's this spring.
What I usually do is polish the sides of the hammer and the hammer cutout, chamfer the cylinder, recut the cylinder throats, polish the chambers, lighten the trigger and hammer spring, and then just simply shoot it to smooth things out. It's not all that hard, but if you are doing just one then some of the tools will cost more than paying someone to do it if they are all set up to do it...
But...
The reason that I ask old verses new...
On this pair of New Vaquero's, everything was already done on them by Ruger... They got it all right all of a sudden... nothing needed to be done except to simply shoot them.