There are 2 methods of mining your play style will dictate which is right for you.

AFK mining is low intensity, you can click the ore node once and you will mine until that node is exhausted or your inventory is full. This method is not the most efficient in terms of exp per hour.

Animation cancelling drop mining is the peak exp per hour and is high intensity. Animation cancelling, you can stop the characters swing animation and force the next swing to start by clicking on the node again once the swing has begun, wait until you see a spark from the node, this is the time the resource has a chance to 'drop' and this is the time we want to cancel the second half of the animation to save time and start the next swing. Drop the resources from your inventory when it is full by holding shift and left clicking on the resources, to save time AFK mine while dropping resources.

The best place to start your Mining career is under the loving gaze of Foreman Bvoric in the village of Ratcliffe, he will buy your ore and give you a Mining skillbook as reward for your efforts. This is the most efficient place until you reach level 20 and can begin mining Iron ore. 3 copper nodes are next to the mine entrance near Foreman Bvoric.

The best location for mining Iron is south of Fenwater village in the quarry, here you will find 7 Iron nodes and 2 Coal nodes a great area for drop mining gaining around 225k exp per hour. Fenwater also has 4 Iron nodes in the main village, it's a great place to mine a full inventory of Iron ore, run across the bridge to the nearby forge and Smith the ore, then you can either run to the general store and sell the Iron ingots for gold or store them in the bank. To get to Fenwater you need to go through Thornhill and have made some progress in the main story quest. If you love mining as much as me and and don't want to waste time on the story quests there are Iron nodes just south of Harshwind village, be careful you may occasionally get attacked by trolls, approx exp gains here around 175k per hour.

Once you reach level 60, and can mine Imberite the hard work is mostly over. At the Old Miners hut in Bulwark you will find 5 nodes, I suggest you buy the hut and place a chest, forge and anvil. Exp gains here start around 700k per hour at level 60, and the hut is so close to the nodes you can bank the ore and still get that amount. As your level increases you will get a higher drop rate so exp per hour will raise even higher, for example level 99 to 100 took 22 minutes to mine just over 1 million exp, so almost 3 million exp per hour.

I have not mentioned coal because it is not as efficient as iron, this is due to the difference in the drop rates of the ore. You will need to mine coal at some point to combine with Imberlite ore to produce ingots, after level 60 is the time to mine what you need (wait until every hit is a successful drop) but I would never mine coal purely for exp it's so much less efficient than other options. There are 7 coal nodes close to the Old Miners hut.

Titan's Blood ore also needs coal to forge into ingots, there are several locations where you can find Titan's Blood there are 2 nodes close to the portal Mountains: Tyrant's Rock Portal (River) this is probably the best place, not so many Ambushers here.

Imberite is much easier and faster to mine than Titan's Blood, you should only mine what you need to make the gear you want, not for exp gains. Ice Mountain Crystals can be found next to the Permafrost Portal in the Ice Cavern, 2 nodes are next to the rocks that you need to climb to find the portal, this area is clear of enemies and the nodes re-spawn quickly.