Odd... I never had a problem with mining, in fact, I got 300 way before I got Lv58 to go through the Dark Portal... lol.
Anyways, I putzed around a lot in areas which had Green mobs, and mined lots of mining points. If you're 'stuck' at a level and can't find enough mining nodes to raise your level, try levelling up your character's level.
If you're stuck on, say, Mithril.. and you can't find enough Mithril... level up about 5-10 levels, and go where Mithril is common, like Badlands... here are some of my favorite spots:
Iron: Duskwood. Not the greatest place for Iron, but many people underestimate how much Iron this zone can produced. Don't forget the mountains in the center of the map... DON'T go into the center, there's a World Dragon that spawns there, and will most certainly eat you for lunch. No, I mean, go around the outer edge. Also, along the southern wall and up by Stalvan's House, and that Spider Cave, you will find Iron sometimes too. Also, Arathi Highlands is also decent for Iron.
Mithril: Badlands, you find a good bit of Mithril there. Best places are down south in the Ogre Mound, and near it in the mountains with the elementals. The Elementals also drop Solid Stones if you're levelling Blacksmith and doing Spurs.
Gold: I usually have the best luck in Arathi, though very rarely you will find this in Duskwood.
Truesilver: Desolace, and sometimes in Stonetalon Mountains, in Charred Vale. Also, Hinterlands has usually been good to me with Truesilver.
Thorium: Un'Goro Crater freaking Rocks. You find Small Veins there, like, Everywhere. Searing Gorge can also produce a fair amount of this, as well as Mithril.
As far as Dark Iron, my suggestion, is to ignore Dark Iron completely. Go ahead and mine it, but sell the Ore on AH unless you're part of a Raiding Guild, or somesuch that can help you get to BRD and the special Forge there.
Dark Iron can and will give you nice levels, just... forget about smelting it.
--Xylia