On the iPhone 14, the main thing is not to rely solely on the built-in stabilization - it helps with shake, but not with blur from lack of light or incorrect focus.
Before shooting, tap the screen where you want sharpness (usually on the face) and make sure the camera has locked focus - often the blurriness is exactly because the phone is focusing on the wrong object.
Of course, wipe the lens (even invisible fingerprints affect it), and when shooting, try moving the phone closer to the subject, but not too close to avoid triggering focus issues - the sweet spot is roughly 30-50 cm away.