It sounds simple, but the logic can be incredibly complex. The patterns can involve:
In a 3x3 grid, the interaction between the rows is the most common logic. Check if the elements in Row 1 and Row 2 combine to create Row 3. If that doesn’t work, look for a progression as you move left to right. advanced progressive matrices pdf
The publisher of Raven’s tests often releases small sample sets to illustrate the format. While these are short, they provide the most accurate representation of the style of the actual test. It sounds simple, but the logic can be incredibly complex