Progression for crafting new items and advancing through the ages in Valheim is nicely tied-in to the biomes you encounter and the bosses within them. It makes the game feel rewarding in a simple way. As you beat a boss, you are given access to items or tools that will help you in the next biome and for gearing up for the next boss. It can be good to prepare in advance to know where to mine and how to mine certain ores. Here is a bit of help to get you started with a quick Valheim mining guide.
Mining Copper and Tin
The first main ores you’re going to be mining for is copper and tin. Upon beating Eikthyr you will be rewarded with Hard Antler. This resource can be used to craft an Antler pickaxe. Once you have your pickaxe, head into the Dark Forest biome and look out for large rocks with copper veins running through them.
Tin can also be found in the dark forest, although it is closer to the shore and the ore deposits are much smaller. They’re a dark silvery colour with some lighter streaks of silver. In Valheim mining both copper and tin allows you to produce Bronze bars. To make the bars you’ll need a smelter and then a forge to craft bronze items.
Mining Iron

Scrap iron is the next ore resource you will want to go after. It can be found in the swamp biome mostly in underground crypts among the muddy scrap piles. However, scrap iron can also be found in chests within crypts as well. Scrap iron can then be smelted into iron bars using your smelter, this will allow you to make iron items. The Antler pickaxe and bronze pickaxe both work on mining scrap iron.
Mining Silver
Next on your Valheim mining journey will be silver. This ore location is in the mountain biome, whilst silver deposits can be found above ground, this is rare, most will be found below. To find the deposits you will need a wishbone which is a reward from defeating Bonemass. Once you’ve located a silver deposit you can get to mining it with an iron pickaxe or better. Once again your silver ore can be turned into silver bars in your smelter. With silver bars created you can craft silver items.
Black Metal

Black metal doesn’t have a Valheim ore location as it is only found as a drop from Fuling mobs. Therefore, no mining is needed in order to gather it. You will only find Fulings in the Plains biome however they will start to spawn in the Meadows and Black Forest upon defeating Yugluth. In order to turn black metal scraps into black metal bars you will need to build a blast furnace.
Mining Obsidian
Obsidian is another ore that can be found in the mountain biome. Unlike silver though, it spawns above ground and is found within the smallish black rocks. To mine obsidian you will need to use an iron pickaxe or better.
Mining Flametal

Finally, flametal ore is found in the Ashlands biome and also requires the use of an iron pickaxe to mine and can be mined from Glowing Metal ore piles. They look like small volcanic rocks. Once mined you can turn the ore into Flametal bars by using your blast furnace.
This is just a quick Valheim mining guide, but it should be enough to get you going on your adventures and provide you with some direction of what to work towards.