Bright, dark and stuck pixels
A bright point is easiest to spot against black. A dark point is usually clearer on white, while red, green and blue can help reveal a subpixel that behaves differently from its neighbors. Clean the screen first: dust and reflections can look surprisingly similar to a defective pixel.
Color and uniformity
Large areas of white and neutral gray make broad brightness differences or color casts easier to see. Look straight at the display from your usual distance, then check the corners. A change that follows your viewing angle may have a different cause from a mark that stays in one place.
Checking a suspected defect
Switch between several colors and return to normal content before deciding what you see. Photograph physical defects with another camera; a system screenshot captures the image sent to the display, not a damaged pixel on the panel. Keep your observations alongside the manufacturer's policy for your particular model.