Stone, coal, iron, gold, redstone, lapis lazuli, obsidian, and... DIAMONDS! these are ALL things you will want in minecraft, for instance, you will want coal for torches, you will want iron for armor and tools, and you will want lapis... wait, No, you probably won't want lapis... anyway, there's not much you can do in the game if you don't mine. here are some tips (From my personal experience of course) for mining efficiently.

• Never dig straight down (this can lead to death)
  
• When mining in tunnels and mineshafts, use "breadcrumbs" (something you can use to mark areas to find out where you are in your mining complex) otherwise ignore tunnels and mineshafts and just make player made mines
  
• keep everything well lit
  
• Mine close to bedrock, around layer 16 or 14 is good.
  
• If you want lots of ores, mine at underground lava pools.
  
• if your at an underground lava pool, put a chest somewhere and put any valuables you have in your inventory in it, in case you die in the lava (it's also a good idea to hold Shift)
  

Some things you might want to take with you while mining are:

• Swords 1-2 (to defend yourself)
  
  
• Picks 3-8 (you'll want a lot if your planing on staying down there long)
  
• Food 10-64 (you don't want to starve, do you?)
  
• Torches 1-5 stacks (keep the area your in light, but use sparingly)
  
• Dirt 32-64 (Dirt can be more useful then you think)
  
• Wood 1-2 stacks (wood can be as helpful underground as it is above ground!)
  
• Clock 1 (you don't NEED a clock, but it can be helpful)
  
• Armor 1 set (protection.)
  
  

~Mego2fast

Quick links to other tutorials of mine:

Woodcutting for Blockheads
http://www.planetminecraft.com/blog/woodcutting-for-blockheads-woodcutting-tips/
Building for Blockheads
http://www.planetminecraft.com/blog/building-for-blockheads-building-tips/


Note- all this information was gained from personal experience. if any of it is incorrect let me know, as this guide is made for helping people and I don't want to give out any false info. Also if there are any grammar/spelling errors let me know, I want people to be able to understand me. Also contact me if you have any other problems with this. And feel free to give me suggestions.

Lastly, I want to let everyone know I will be making more guides.