​You don’t get better without practicing. In fact, if you don’t practice enough you’re likely to get gradually worse as your brain cannot build and utilise its muscle memory. However, you have to practice quality. 

How well you execute your shot is key to consistent grouping. There are two points of contact between you and your equipment, one of these is your release hand with either your string or your release aid. Your execution then, is vital, as it has a significant effect on how well your arrow flies from your bow.