Clean the lens before every session. A fingerprint can make even a good camera look soft and hazy.
Open the camera settings and enable the grid. Learn how to switch lenses, set focus with a tap, and adjust brightness by dragging the exposure control.
Avoid digital zoom when possible. Move closer or use an optical lens option such as 2x if your phone provides one.
Practice by photographing the same object with each lens and compare detail, perspective, and background.