Woah... stop right there. There's absolutely no right, wrong, or recommended method... it ALL depends on what you want.
There is no reason to underexpose, and ordinarily, over expose. It's all down to what you want to achieve. In the shot above, where you have a very bright sky, slight under exposure would have been beneficial. In a shot where there are predominantly dark tones and few highlights, then slight over exposure would benefit.
However, the D800 has a very wide dynamic range, and unless you're in extreme exposure circumstances, AND you know what you're doing, I'd expose how the meter suggests when on matrix metering.
Over exposing will reveal more detail in darker areas at the expense of the highlights, and under exposure, the opposite. If a subject does not make use of the camera's whole dynamic range (doesn't fill the histogram) then you can shift everything up (ETTL) or down (ETTR).. but you need to fully understand what you are doing here. Research "Expose to the left" and "Expose to the right" to fully understand this.
Seriously though... you've got 14stops of dynamic range.... just use Matrix metering and do as the camera suggests until you've fully researched this more.
What level of experience would you say you are at? Just so we know at what level to pitch the replies.