I think it's a combination of several things, Nicole - how you hold the camera, how you focus, and which screen you have. For me, however, the tack part of "tack sharp" has always been a matter of using the little pop-up magnifier in the standard waist-level finder, or using a reflex finder and the accessory view magnifier.
The focus ring of the 80mm lens sits fairly close to the body, making it less convenient to focus (for me) than some of the other Hassy lenses. My approach is similar to what Gary is suggesting. I take meter readings first, set the exposure and pretty much leave it at that unless I see major shifts in the light. Then, I preset focus to the general distance at which I'm working, and then do "follow-focus" with my eye glued to the finder. I support most of the weight of the camera with my right hand, thumb on the top of the body and middle and ring fingers gripping the far edge of the quick-coupling tripod shoe. That leaves the index finger free to operate the shutter release. I focus with the thumb and middle finger of my left hand, using the left hand only to steady the camera, not support it.
There is also a focus ring accessory available (part #51700) that slips over and tightens to the focus ring. It adds a fold-out lever that many find handy for quicker focusing. I don't have one, and have never used it, but I've heard enthusiastic reports. Also, there are various focusing screens available. Personally, I prefer the split-image screen, as it is easier for me to see precise focus with that screen. Personal preferences vary, however. If you can find one, you might also find the older #45072 Flashgun Bracket 1 handy. It's an ergonomic handle grip with a leather strap that fits over the left hand, and has linkage that operates the shutter via a trigger on the handle. Using this, all of the camera weight, along with tripping the shutter is done with the left hand, and the right hand would do the focusing. Neither of these are listed on the current Hassy page, so I'll try to scan part of my old 1991 catalog, and post a link later.
One thing you want to be cautious of, however you grip the camera. Avoid putting pressure on the winder knob as you operate the shutter release. If the rewind has tension on it when the shutter is released, the lens shutter and body can get out of sync.