Couple of "hints" that I picked up from reading my brains out before I mounted my 140 pound plasma on an articulating mount that must've weighed another 60 pounds. I've only ever done it that one time, but I found this to be helpful when I did it, so since you're asking, I pass it along.
First, it's critical to hit the center of the stud. Studfinders, by and large, are decent at finding the general location of the stud, but not perfect; same is true for the studs are 16" apart, so find one, measure 16", and find the other. Both of those methods may help you find the general location of the stud, but since it's important to be dead center, what I did (at the suggestion of others), was find the "general location" of the studs, then used finish nails to "feel" into the wall until I knew exactly where the outside edge of each stud was, then I drilled my hole right in the middle. Might've been overkill, but it was the only way I could be sure of where dead center was.
Second, make sure you drill a big enough (but not too big) hole for the lag screws/bolts; you don't want it to split the stud, but you also don't want the hole to be too big for obvious reasons.
Third, don't overtighten when you screw in the lags.
Fourth, the more studs the better. I got kind of lucky/unlucky. Unlucky in the sense that because of various mechanicals in the wall (ventilation, etc.), my studs weren't 16" apart on center; lucky in the sense that because of this, some of them were closer together than 16" (even though others were further apart) and I was able to mount to 3 studs rather than the suggested 2.
Fifth, draw it out on the wall EXACTLY where it's going to go before you start drilling. You're likely only going to get one crack at getting this in the "right" place, so it's critical to measure everything and know where everything will be.
Sixth, if you're going to do any in-wall wiring, know exactly where the boxes are going to go (and that the location "works" with what's inside the walls and where the TV will be); draw that out too (paint and spackle are cheap).
Seventh, line up the mounting holes on the back of the TV in relation to the holes for the lags on the wallplate for BOTH vertical and horizontal orientation (although horizontal orientation is probably less of a problem since you can probably fix it a bit by sliding the mounting bracket left to right on the wall plate), and make sure that you put the wallplate in the right place on both axes to make sure that the TV will be in the exact spot you want it at the end of the day. I made the mistake of misjudging this (even though I had measured repeatedly) and, consequently, my TV sits about an inch lower than I had intended for it to be (couldn't really adjust the mounting brackets vertically with my TV, but that's a different story). Fortunately, that was the only material mistake I made in my install, but I had planned for months and months.
These are all common sense things, but if you're like me and this isn't exactly your wheelhouse, it's important to keep them in mind.
Good luck!
--Mav
