Hiring a soundman for one is an obvious measure. But for OMO, using good lavalier mics like the Senny G3 is a good workaround. One set per talent. One channel per set. In post, replicate the mono channel in use during dialogue and eliminate the unused channel during silent pauses. This dramatically reduces background noise. Use external recorders (eg.Roland R-44) if you have more talents (talking in the same shot) than you've got channels on your camera. For situations where you don't want the lavalieres to be in-shot, Use fabric tape to paste the lavalier onto the inside of the talents' garment. Sticky side to garment. position the mic-head in the hollow of the collarbone or between the breasts. Float the mic head where there is no contact with skin or cloth to avoid rustling. There are expensive moleskin solutions available commercially, but the fabric tape seems to work well too.
The audio quality from a directional lav has a distinct clean and "near" signature (with a variable noise floor depending on the distance from the mouth, sensitivity settings of the transmitter and AF output settings on the receiver) that may sometimes sound unnaturally "bright" especially if it is a extreme wide shot, but it beats muddy audio with noisy background.
For lone gunmen who swear by their Rode shot gun, quality can be greatly improved by using multiple mics instead of just one. Again, one for each talent and onto different channels. Lone gunmen's best friend is the boom pole on a light stand. But the assumption that aiming the mic downwards from above the talents head will eliminate the most noise, don't always work. Hard floors can bounce more noise than high ceilings.
Rode shot gun's biggest weakness is the unbalanced 3.5mm output. Extending that cable will introduce horrible hiss. It's better to extend the range with either UHF or bluetooth transmitters. (but not both at the same time due to lag issues)
Another alternative is to pair an XLR shotgun with the Senny SKP2000 XLR transmitter (no cables at all!)
The other source of noise is the camera's AGC circuit, so its best to switch that off or use a good micpre and external recorder if AGC cannot be disabled. Even if AGC can be disabled, a good micpre (Sound Devices are great) can still improve the quality of the recording (especially with low talkers) by boosting signal strength while keeping hiss to a minimum.
