Summarize the following:
So you have a diamond pickaxe, a fortress the size of New York, and enough ore to make Scrooge McDuck envious. Now's the time to get serious. Enchant your pickaxes to improve their mining ability. Here are all enchantments available for tools:  Fortune (max level III) increases the amount of ore you get per block. If you are lucky enough to get this one, save it for the extra-valuable ore only. Note that you cannot get Fortune and Silk Touch on the same item. Silk Touch (max level I) mines entire blocks instead of ore. You'll need to mine the ore with a different pick to get the ore, but this does save on inventory space. It can be more valuable than Fortune if you're on a large multiplayer server and plan to sell the blocks.  Efficiency (max V) speeds up mining and Unbreaking (max III) increases durability. . Once you have diamond armor and a diamond sword, you may be ready to build a Nether portal. The area on the other side has several new blocks to mine, notably Nether quartz. There's nothing unusual about the mining itself, but be prepared to face very difficult enemies. . If you don't mind laying tracks and tinkering with redstone, you can make your own subway system to transport goods. By digging branches off of the main subway tunnel, you can stay near your tracks and never run out of inventory space. See the linked article for details. Strongholds are the rarest and most valuable structures that show up underground. Look for mossy or cracked stone, which could potentially lead to a system of libraries, prisons, and chests. Each stronghold has an End portal which can be activated to reach a special endgame zone. You can find the strongholds using eyes of ender, gathered from the Nether. This technique is complex, dangerous, and requires a great deal of preparation. Most players will never even consider attempting this, but if you pull it off, you can mine incredibly quickly. Here's the gist:  Enchant armor with at least Protection I. Brew splash potions of poison and regeneration. Attract silverfish from the spawner found next to End portals. Construct a tunnel of glass so they can follow you without burrowing to you. Prepare a high glass walkway in the next area you plan to mine. Build two Nether portals here, one for you on the walkway and one for the silverfish below you. Lure the silverfish through a Nether walkway to the portal you just built, so they reach the area you plan to mine. Throw splash potions of poison and regeneration on the crowd of insects. They will get hurt constantly but heal before they die, summoning more silverfish from the stone around them. In just a minute or two, the silverfish will mine through a massive area of stone, leaving the ore behind.

Summary:
Enchant your pickaxe. Mine in the Nether Transport your loot with an automatic subway Attack strongholds. Make silverfish mine for you.