First make a staircase to the bedrock... Then every 2 steps make a side tunnel on each side of the stair-case! Then you will eventually find many caves and maybe even a stronghold if your really lucky! I use this way to mine and I say that this is the best style of stair-case mining I have ever done! P.S. Try and make a branch mine at the bedrock so you might get more diamonds! If you found this helpful please give diamond!