The main focus (pun intended) is on how to improve the low light focusing ability of a camera. There are a couple of ways to improve the focus:
1. Do it manually
If you're dealing with stationary subjects, then manual focus may be viable. It can be quite tricky on lenses which are not designed for manual focus - but may still deliver better results than the AF mechanism of your camera.
If your camera has it, you may be able to use 'focus confirmation' in manual focus mode to make things easier.
2. Add more light
The other option is to add more light, so the AF has something to focus on.
2(a). Better Lens
Really this is just improving the amount of light your camera has to work with - the camera body will evaluate the AF with the aperture wide open, so even if you're not using a wide aperture when taking the shot, you'll get better AF from a lens with a better wide aperture.
2(b). AF Assist
This is also another way to add light - many cameras have a built in light which assists the autofocus. Your camera should have one - make sure it's properly activated. In my experience AF assist generally works well for short distances, but for longer distances, I always carry a seperate light source.
2(c). Manual AF Assist
I work outdoors in the dark quite a bit, and carry a big 'spotlight' torch - which I can use to highlight the focus point for the camera. If you're dealing with moving subjects, then a friend or assistant holding the torch to track the subject while you take photos makes a big difference (although you'll definitely want a flash for a moving subject)