I just fell into a deep lake underground and miserably died because I was not able to jump out. Are there any techniques to survive in this case, or is this one of the dangerous aspects of being a miner?
If you're lucky enough to end up in a lake with rock or dirt sides (not sand) you can dig 3 sideways into the bank and 2-3 up to create an air pocket to jump up into:
######~~~ ###++#~~~ ###++#~~~ ###~~#~~~ ###~~~~~~ ###~~~~~~ ###~~~~~~ ######### # = Dirt / rock / other block ~ = Water + = Precious life giving air
From there you can dig your way out. I've done this so often I can now do it in pitch black darkness. Maybe I should learn to look before I leap...
If none of these options are available, you can try digging an air pocket, as explained in this answer.
Build a solid area around yourself with mud or dirt, make the ceiling 2-3 blocks high, then mine out an air pocket.
This is sort of like Stuart Pegg's answer above, but doesn't require a solid wall next to you.
NNNN NXXN N N N N DDDDDDD DDTDDDD D - dirt N - new dirt you add X - spots where you add dirt, then mine it away T - mine this spot out and put a torch there, so you can see
sjohnston has listed some great items, but if you lack those you can drop sand below you to try and get up.
This is going to be another air-pocket answer, but for a situation where the lake is particularly large, and no nearby wall is available.
If you have the misfortune of falling into the middle of a very large lake, break out your pickaxe and immediately dig yourself down. Be careful if the water starts to flow out, as that means you've hit the bottom of the lake and now need to either wait for it to drain, or very carefully fall out of it yourself, taking caution not to fall into something even worse.
If you dig down five tiles and still haven't hit another cave, immediately dig three tiles to the left/right (whichever one offers you a solid cave) until there's a space where you can stand under two tiles while still having one tile next to them. Dig the two tiles out from above you, careful to leave two tiles and the outer 'lip' intact, and start jumping. You'll slowly recover your air and can work on a better long-term survival/escape strategy.
Y = You _ = Surface D = Dirt X = Area to dig ____Y___ DDDDXXDD DXXDXXDD DXXXXXDD DXXXXXDD DXXXXXDD DDDDDDDD
One of the simplest early game techniques that is available is carrying ropes or rope coils (made by crafting 10 ropes together). Simply place them and climb! Another alternative is to use platforms to make stairs. You can also put many platforms over the entire lake, so you don't have to worry about falling in in any longer.