On this page of the guide to Resident Evil 3 Remake, you will find tips on how to score headshots more effectively to kill zombies faster. You will also learn how to miss less often to waste as little ammunition as possible.
If you are fighting ordinary zombies and it is impossible to avoid them, then the best way to attack them is to aim at monsters' heads. The exception is when, for example, there are explosive red barrels in the area that can kill nearby monsters with a single explosion.
Try to keep a better distance from the zombies so you can aim at the monsters. If you are fighting at a medium or short distance, you may have much less time to aim at a zombie's head. It can also happen that the undead unexpectedly leaps towards the hero and forces you to dodge or resort to melee combat to protect yourself.
Before you fire your first shots, observe how the zombie moves and what movements their head makes. This will allow you to better "predict" its position.
As you make progress through the game you can find some weapon upgrades - some of those increase accuracy and reduce the weapon recoil. For example, you can find additional scope and weapon sight or a special weapon handle that will reduce the recoil while firing. All newly acquired weapon upgrades should be installed immediately - none of them are mutually exclusive.
If you still have huge targeting problems and miss a lot, you can use the aim assist to help you track down monsters by "locking" your sight on zombies. The Aim Assist option can be found in the game options under the Controls tab.