The length of your arms (humerus, radius/ulna bones) will be an indication of how close or wide you will grip the bar. Generally longer arms will allow a wider grip and shorter arms a closer grip. The exception to this general rule would be in a Barbell sport such as Powerlifting where one would often aim for the shortest bar path, hence the widest allowable grip regardless of arm length.
But if you just want to utilise the bench press movement to strengthen your upper body, specifically your pectoral muscles (pecs), anterior deltoids, and triceps then you would use what is considered a neutral grip. The wider your grip the more your pecs are stretched and the harder the movement becomes, the lighter the load must be. The closer your grip the more the pecs are flexed and the less force they can produce, outsourcing the major portion of the movement to the triceps, and again the lighter the load must be. So if you want to benefit all of the aforementioned muscles then neutral grip is likely the most effective way to go about it and the one that you will be able to move the most load with.
To find a neutral grip width you can utilise the smooth rings on the Barbell to give you a measurable gauge, but a good indicator of neutral is that, at the bottom of the movement your elbows are under your wrists and at about 45 degrees to your torso which is lying on the bench.
Try to hold the barbell deep in the palm of your hand so that it aligns with your forearm bones (radius/ulna) and doesn’t sit behind them during your press. Make sure your externally rotate your shoulders and try to snap the bar like you would a stick. Aim to punch (controlled of course) your knuckles toward the ceiling as you press and safely control the weight back to your chest when doing multiple repetitions.
Hope that helps. If you’d like to know more please ask your coach or shoot me an email.
Happy benching and see you all in the gym!