All good advice Nick - you need dark skies and low magnification, and averted vision will be your friend!. I observe with smaller aperture than yours in good dark skies, and there will be hundreds if not thousands of galaxies within your reach! But practice is very important, and don't expect to see more than faint smudges when you start out.
Centaurus A can be difficult, especially because it's such a familiar object to us Southerners, with images of it all over the place. I couldn't see it at first, until I realised that the faintest of smudges I kept passing over must have been it. With more views, I began to notice that it appeared truncated on one side - this was the dark lane starting to register on my eyeballs/mind! Even now, I need the very best of skies to see the 'dim side' of the galaxy, but it is rewarding when I do.
You will find many other galaxies much easier to see than Centaurus A. NGC 253 is probably the stand-out Southern galaxy for new observers when it is around in our skies, but there are several others almost as good. As stated before, Sombrero galaxy is a good one, although very small.
If you can join a local astronomy club, you will get access to a wealth of knowledge and experience. Good luck with your viewing!
Cheers -