I dig a diagonal shaft down to the bedrock, then work in strips every few vertical steps going either side of the shaft, it's worked so far in the two shafts I've dug - I've found gold, diamonds and tons o' coal and iron. I've found a fair few caverns as well.

General question - last night I was buggering about in a cavern (YJ) and fell into lava, I used the /back command when I respawned but couldn't find the stuff I was carrying - does that burn up in the lava, or would it exist still, but be bobbing about under the surface?

How far do you dig out horizontally?

To stop me going too far I dig as far as a stone pick takes me.

I don't go too far - I try and stick to a system, so I would dig the first gallery with the ceiling as level 16, and go about 25 blocks, then keep adding galleries spaced 3 blocks apart until I have 10 or so in parallel; I'll then go below my starting point and dig a parallel setup in (hopefully) the same xy layout, so that the floor between them is one block high.

When I finished that, I'll go back to the level above and expand the first shaft another whatever blocks, rinse and repeat. I think all this ensures I find virtually everything in that space, and it seems to be quite scalable as long as you can find your way back... Putting torches consistently on one side helps with that.

Nice, I'll try that technique out.

Providing everything's nice n'tidy navigation shouldn't be too hard - maybe just a torch showing where the main staircase shaft is. I can see what I'm mining even when there's no light source around.

Hmm, maybe my brightness is set too high. T_T