I usually go to layer 9ish and strip mine, but other people have better luck with other methods!
by the way, I'm not sure if you know, but if you hold Shift and F3 you get your co-ordinates up in the left corner, the Y co-ordinate is your level, easier than counting up from bedrock as you can never be sure what level your at to begin with!
Diamonds spawn on layer 16 and under, and lava lakes 12. So if I have zero luck with cave systems (which I prefer before strip mining) I go mining on layer 12 just so that I can easily block off the lava lakes
The Darkness will win one day, and light's time being the winner is nearing it's end. Because light is overrated.
IntelliJ > Eclipse because better autocomplete and inbuilt command line. Oh, and use the latest version for mods.
My heavily work in progress Minecraft Modding API and mod loader, N-API: https://github.com/Niadel/N-API
Code changes from 1.7 to 1.8 for us modders (that I found): https://gist.github.com/Niadel/2d2db8dd89de27f970a7
No, lava starts at level 11. Mine down so that your feet are at y=11 exactly, then start strip mine or feather branch mine (my favorites).
Major bump, but I mine as well say that I usually make a 3x4 staircase mine down, then dig 3x3 shafts around the world at y=11 (feet level). That was I'm right above the lava and it doesn't flow into my shaft, and I can still find lots of diamonds. Then I usually fancy up the shaft with oak wood planks and fence post similar to an abandoned mineshaft, but not abandoned and with a complete rail track
Usually I start with a strip mine at levels 9 to 11 (3 blocks high), and make every strip of the strip mine three blocks away from the other (three blocks in between tunnels). Then when I have made a large enough mine that it takes way too long for myself or anyone else to run to the end, I dig down four blocks and stagger the other mine by two blocks to make the most efficient "viewability" of the stone around me.
The strip mine, at a cross section view, would end up looking somewhat like this
Where S=Stone and _=Tunnel(Air)
I find it quite fun, and with some effort I can usually find at least one ore of Diamonds in 15 minutes
PS I also decided to dig the tunnels three apart from each other as most of the time ores spawn in two wide formations, allowing for not too many ores to be lost in the blocks not exposed to the eyes of the tunnel digger(s)