Revised way (From world creation):
1 Get some wood, fast. Make a pickaxe and find a cave opening with a crafting bench on you) Obtain 12 stone and make a stone pick.
2. Look for iron on the walls with your brightness maxed out, mine the first ore vein you see. You'll need 3 ingots.
3. Make a furnace and put your spare wood in the fuel slot, the ores in the other slot. Once these are done smelting, Dig straight down (cross your fingers) and mine until you've hit y=12. Either strip mine or look along cave walls. until you find your precious loot before you even make a home.

if you dig staright down, there is a 50% chance that yyou will fall into a raven, lava, dosen of mobs.

I recomend making a staircase

You should add a video of this working for you so that people see that it works. Thats now what I do to find diamonds though.