Grind improoving is always done by chainging the yoyo but you can improove your hands to do better grinds, I just took one of those hand softening creams and left it on my hands for 5 min then washed them 2 times, my hands were really smooth and that improoved my grinds.
Baby Powder also works…
But I don’t think you’d like any baby powder getting in your bearing…
No, I meant baby powder in your hands…
I just keep my arms really clean
I know. There’s just a probability that the powder might get into the bearing.
rubbing a chalk doughnut (for playing pool) on my hands worked
i coat my hands and yoyo in thin lube and butter
Hmmmmmmmmmmm…
Hmm… Personal highgene is important… Even for your yoyos.
Crisco, even better Motor Oil 
(j-k dont do that) 
hand lotion i would say is the best longterm solution
That would make metal blasted yoyos grind worse. If it has a blast, the blast would be wiped off durring the satin.
-James Reed