An individual dwarf's preferences are also worthy of note. A metalsmith who likes a particular metal is more likely to produce higher-quality items when working with that metal, and if they get a Strange Mood (and you have smelted that type of metal in your fort before), they will absolutely insist on making their artifact out of that type of metal--nothing else will do (unless you use {forbidding} tricks to slip in something else). Similarly, a metalsmith who likes a specific type of weapon/armor is more likely to produce a higher-quality version of that type of item, and if they get a Strange Mood, their artifact will be that type of item.
So, if you want masterworks: Check your dwarves' preferences, and see who likes what metals. Candy is obviously best, but how soon can you get it? Find some guys who like the metals you can work with now. Correlate each individual dwarf's preferences, so you don't risk wasting a potentially very valuable mood on a useless artifact, like a silver breastplate. (Note: Making one "ridiculous" artifact ranged weapon, like a candy crossbow or featherwood blowgun, is actually quite advisable, as it's a great weapon to give to your Hammerer/Captain of the Guard. Never have to worry about beatings again, and they're still very effective against actual enemies.) If you have the dwarfpower (with the correct preferences), try to have a different smith for each weapon & piece of armor: One woman makes axes, another guy makes low boots, their neighbor makes mail shirts.
If you want good artifacts: Largely the same as above, but applied to a broader spectrum of dwarves, and looking more towards the future. If a dwarf likes a good military metal that you don't yet have in abundance, try to acquire just a little--usually, by importing steel or platinum. Keep that metal safely forbidden until you need it. Next, give each of your "chosen" a little bit of the appropriate metalsmith training, just enough to exceed any other moodable skills they may have, and then have them do non-mood things, like (almost) the entire Farming menu, for the rest of their life. And finally, wait.