Without knowing all of the details or seeing examples of the problems, here are a few thoughts that come to mind:
You noted the models were moving, so you'll want to use the Continuous Focus mode (Nikon's term - Canon calls this AI-Servo). Once the camera obtains focus on a subject it will attempt to "follow" that subject and make focus adjustments so that the subject remains in focus.
If it was dark, the lack of light can impede autofocus operations.
If you're photographing a moving subject, without flash, indoors, with an f/2.8 lens there's a good chance that you might have been getting motion blur. You don't note what shutter speeds you were seeing (higher ISO would've allowed for shorter shutter speeds), but you might've needed a faster lens for such a situation unless you cranked up the ISO quite a ways.
I haven't done any runway for a very long time, but I'd assume the same trick still works: focus where they're going to be and shoot 'em when they get there. That is to say that under less-than-ideal lighting, manual focus (or autofocus at a preselected point, disbled during shooting) is probably your best bet.
It helps if you can catch the models at a pivot point; there's generally a bit of a freeze pose or two at a turning point (whether at the end of the runway or at the ends of aisles in a meander floor show), but if you are stuck in the middle of the runway somewhere, you can pick a couple of marks to shoot for. Count on bursts both to get the best chance of good focus and to catch something other than awkward postures (or bad draping, accessories flying about, etc.).
Depends on the specific problems you've had, but a few suggestions:
Shoot in manual mode. The models are probably far better lit than the background, so depending on your framing your exposure will change with every shot and you'll have to do something different in post-processing for each. Easier just to look after it yourself.
Aim for 1/250th. Don't go below 1/160th - it'll be motion blurred. You can get away with high ISO as long as you get a good exposure. High ISO + still having to boost it in post-processing is bad.
It depends on your position but you're unlikely to get sharp full body shots at f/2.8. Stop down a bit. Of course that causes low-light problems. You just have to find a balance.
Set up AF-ON / "back button focus" to separate the focus function from the shutter release. Focus on a mark once, then wait for the models to come to it. If you have to change mark in a hurry or you want to track the motion you have the AF-ON button (make sure it's in AF-C mode). Or learn manual focus.
Use Continuous-High mode and shoot bursts of 3 to get decent change of a natural balanced pose, as well as the best chance of catching a focus sweet spot without motion blur.