I have been on the server less than a week, so I don't have an eff7 yet, just using a max'ed fortune.

Y: I mine at y=10. Yes, I know... lava. But I'm not phased by it anymore. I like 10 with a 3 high tunnel because you are exposing y= 9 10 11 12 13 which I think are the prime locations for diamond (just from looooong mining experience).

Method: I do a long 1/3 tunnel. then I skip 3 blocks, and branch out from that main tunnel both left and right. Basically expose the maximum nodes while breaking the least stone. It works for me.... I get great results with this method and have used it a long time. 1.8 worlds have big nodes so I think 3 is the perfect spacing.

When I find an untouched cave or mineshaft, I explore it.

I always use night vision potions (quite easy to get mats-- golden carrots go a long way, you mine plennnnty of gold with this method to reck blox.

Use a boat to go out to the border. Then work back the other way. Keep your /home updated where you "leave off' mining, and just keep pressing on from your same spot. This way you are always covering new ground. I always head east or west, for example, with my branches going off N and S.