You will be using your pickaxe and bombs to break rocks. Then you want to switch to farming before you fall asleep at work. In the Skull Cavern, you want to prepare ahead of time with Galaxy Sword if you are lucky or the Lava Katana sword from the Guild, maybe some high power rings, multiple stacks of 999 stones for staircases, and a stack or two of food (maybe special food to boost luck etc) to pursue ultra-rapid descent with Staircases to where your desired materials are abundant. Then you want to pursue farming to get ore, minerals, gems, artifacts, and experience. In rapid descent, you want to unlock 10 or even more floors per long day while ignoring anything that doesn't help you descend.
In The Mines, you want to pursue rapid descent to unlock the elevator to the floors that hold your desired ore and to upgrade your armor and weapons beyond the ability of the monsters on the floors where you want to farm ore. This page is mostly about strategies for The Mines. Your mining strategy depends on which mode you are in. The modes are generally referred to as "descent" and "farming".
Your current mining mode determines your choice of strategy. Mine iridium ore and Prismatic Shards in the Skull Cavern at Calico Desert via a Bus ride later in the game. Mine copper, iron, and gold ore as well as gems and artifacts in " The Mines" in the northeast corner of Stardew Valley. Just give yourself plenty of time and take and eat plenty of food. But early in the game, you need to descend to at least floor 80 of The Mines to unlock ore for upgrades and sprinklers, so even sunny days with neutral luck may have to do as long as you are managing your fields well to finish your watering before 9am.
Rainy days with good TV luck are perfect to go mining as you have not exhausted yourself watering plants and you will find ladders faster.
This will suffice for combatting your first few slimes, but you’ll be given better weapons plus armor as you advance. When you do go to the mines for the first time an adventurer named Marlon will give you a Rusty Sword. You can’t get to the mines until the 5th of Spring, Year 1, when you will receive a letter saying that Joja-corp has cleared the path to the mines. And you won’t get the monster drops that are needed for the Community Centre - though Joja-Corp will be happy just with your money … seriously? Go mining! And you’d probably be buying a lot of stone from Robin. You would still have to put these through a furnace yourself, and you can’t get Iridium from Clint. It’s possible to bypass the use of the Mining and Combat Skills by buying coal and ores from Clint the blacksmith. Which also means Combat, although Combat is very simple in this game. Until you are filthy rich, the way of getting this is to go Mining. And many of the items you’d like to craft in order to build up your farm - like sprinklers, tappers and kegs - require metal. This will help you get your farm moving faster, but you need the right metal. Most of the tools you start the game with can be upgraded into more effective versions, which chop down trees or break rocks with fewer hits, or where you can long-click to water or hoe a larger area.