Don't get frustrated....we all are going through a learning curve. I have attached a few shots that I was working on today. They are sized small to fit into this forum but you can also check my gallery via the link below.
I found that for me it is in the settings and my technique. If you are hand-holding you have to be steady...test your first shots with a tripod to prove to yourself that the camera is fine. Then when you start hand-held shots to check your hand-held technique set your AF to AF-C not AF-S....again as a test only. This will keep your in/out sway from taking your focus away from your subject. The D800 resolution is sensitive. Start with relative close up shots...I am assuming those are the ones you have a focus issue with. If it is landscape then go ahead and do the closer shots and move to landscape or 'cats'. Give those few things a try then come back and respond. I had to try out all the settings until I was satisfied with my set-up.