So, you're probably wondering why I'm making such a weird topic. Why should I pick up a sieve? Why should I stuff my inventory full of ores, ingots, and plates? Well... the answer to that depends on what you plan to major in. If you're looking to go into melee combat or magic, this guide isn't geared towards you. (It can help warriors and fighters a little, but you need to focus on Strength if you're a warrior or Will if you're a fighter more.) But if you're looking into Bard or Ranger, this is a must read.
Why you should train these skills.
Refining and Metallurgy both give bonuses to Dexterity as you rank them up. Metallurgy's boosts aren't as good, but ranking it will expedite the process of ranking refine, as it will eventually allow you to pick up as many as three ores with one use of the skill, and if you have a Spirit Weapon, the massive amounts of gems you're sure to find in the process will really help make the spirit stronger. Refining, on the other hand... if you plan to take up Blacksmithing for whatever reason, being able to make plates on your own will certainly help. But there are two reasons why you should train Refine.
1. It gives a LOT of Dexterity over the course of ranking it up.
2. The skill is very hard to train. Which brings me to my next point:
When to train the skills.
You want to train the refine skill as soon as you possibly can. Starting at rank C and lasting until rank 5, you will be required to
FAIL the skill in order to advance in ranks, and if you start training this skill late, you will find it very difficult to proceed with only a 1% chance to fail. Training this skill will be something of a money sink, however, so I recommend having at least 50-100k gold combined on hand and in the bank before starting. Metallurgy, you won't be able to train until you have cumulative level 6 exploration, which can be remedied by finding a 1,500 EXP Lost Elf or something, then doing the level 5 cap quest. You only need novice rank (learned by equipping a sieve) to find metals, but having higher ranks will improve the success rate and allow you to find more metals at once. So in short, start as soon as you can.
HOWEVER. With the implementation of the new talent system, getting r1 in both of these skills too early may put you at a severe disadvantage, as the combined talent EXP from these two skills appears to put you at level 11 or 12 with this skill. Come G17S3, at least based on the implemented Korea version, the difficulty of Shadow Missions (and thus presumably storyline missions from G9 onward) will be based on your highest level talent. A level 11 talent or higher will put you on hardmode. So if you decide to rank this early, rank it alongside with a combat talent of some form so you can actually fight when it comes time to do the storyline. Alternatively, you could just get the storyline out of the way early, but that won't help you when future installments come out.
How to train the skills.
It's recommended to take on the Blacksmithing talent for this. The x2 training experience will be invaluable to you as you work to max refine, plus you'll gain levels rather fast while using metallurgy. You'd be surprised how many levels you can gain in a week's time. It is also recommended to find some enemy somewhere that has high attack and get slaughtered by it. Take 500 points of damage with a single attack, and you'll be given a title that will reduce your dexterity by a whopping 30 points, which comes in handy while trying to fail. Alternatively, if you by this point have completed G13, you could also use certain Persona skills to reduce your Dex even further.
First off, to actually unlock the skill, you'll need to do a part time job for someone (I know Elen in Bangor and Meles in Filia, but I don't know who it is for Giants. Probably their blacksmith in Physis.) You're limited on time as well, so complete it as fast as you can before the quest expires, and you'll learn the refine skill. It's probably easiest to do Elen's mission, since Barri Dungeon's easier to find than Ant Hell.
When you have the skill, start working on it immediately. You will want to focus on this while your skills are relatively low, especially your Production Mastery. You don't need to fail the skill until rank C, so things may be frustrating at first, but you will thank me for it when you get into the numbered ranks. For actually finding the ores to refine, I tend to go to Port Qilla beach and use metallurgy there, as the area is big, there are numerous ore deposits to sift through, and you don't need to change channels to keep finding more. The only problem is the time; it's rather hard to see the mineral deposits against the water when the sun is burning bright in the sky. It will take a long time, but once you hit rank 5 in the skill, you can breathe a sigh of relief, as failures, while still something you can use to train, aren't actually required to get the rank up anymore, and at rank 1, you don't need to fail at all as you work to master the skill. (Unfortunately, the success rate of Mythril Plates is still crap even with 200+ dexterity and decent Production Mastery; on good timing, I can probably get a 51% success rate with that.) If you feel the going's too slow, ask others with high ranks of metallurgy to help out. Heck, if you catch me on, I'll even help you out some. I have refine and metallurgy mastered now, so I can give you everything I find. Would be nice to get a few iron ingots in return, though. Need to rank Blacksmithing. XD
Alternatively, there is an actual Mining skill now, so you could theoretically train that while training refine (though you'll probably be spending time in Sliab Cuilin for higher ranks), but the skill adds to Strength, not Dexterity. Still, ores from mining in Barri Dungeon can stack to 50 now, so they technically take up less space for the same amount. I still say get Metallurgy trained and work on Mining as a side project when you have the AP or are getting holy water from Comgan because the blacksmith in Port Qilla broke your sieve one time too many.
I hope this helped somewhat. I did my best, but this is pretty much the only area of Mabi I really know anything about because I've worked on it for so long.