Welcome to the Bunnings Workshop community @Redbomber85. It's fabulous that you've joined us, and many thanks for your question.
For your bush/hedge not to look hacked at, it needs regular maintenance. There are a couple of things that need to be done to maintain a hedge's shape. First, you need to establish the basic shape, and this might require a hard prune back if the plant is overgrown. This can be the hacked situation you are envisaging. Not to worry, this is just the base structure of your hedge and will be covered up the following season. You'll then prune the new growth each year to establish the form of the hedge. It's a great idea to prune late-spring, so the recent growth doesn't harden and become woody. If you wait the full growing season before pruning, you'll need to do a hard prune, and the hedge will look bare for a while.
When you are beginning to use a hedge trimmer, it's a great idea to stretch out a string line, so you have something straight to follow along. Even some of the best gardeners use a string line to establish a perfect hedge. It is also important to feed your hedge, as it will allow it the energy to fill in any locations that are a bit patchy, and I'd suggest Scotts Osmocote Landscape.
Let me mention the very knowledgeable @Adam_W to see if he has any hints or tips on getting a fantastic looking hedge.