Temporarily bumping up the gain can help but low light is always tough.

Do you have peaking or crisp (depends a bit on the brand how they call it) enabled? It might start to target the noise if your camera is sensitive to noise upon higher gains, but it can help you reach correct focusing. If you work from the shoulder, try to mark two of your most prominent positions on the lens focus ring by using a "tent" of gaffer tape. That way you know whereabout you are focus wise when moving. When working from a tripod, try to learn the direction of having to turn for focus so that you are quicker capable of correcting for mistakes by noticing what elements start to become in focus. In some cases, the focus mill will be digital and the same trick for the focus ring on the lens will not work, but a good way to learn (at least how I was taught as a tip) is to learn to count the amount of rotations your focus mill needs to make. In all cases however, you will probably not be live all the time, unless you are in a single camera setup, and the best option you have is a quick zoom in, focus and back out immediately to frame your shot. But in all cases: low light is just simply problematic. And the thing that basically happens every time in theater-like settings is the amount of light being chronically "not enough" :P .