Choose the area the group will occupy
Treat the group as one arrangement before choosing positions for individual pictures. Measure a proposed overall rectangle on the wall and note the furniture or architectural features around it. Decide whether the group should feel centered on the wall, a sofa, a desk or another feature. Those reference points may not share the same center.
Collect the outside dimensions of every frame, including pieces you already own. Use those measurements in the plan rather than the dimensions of the images inside them. A narrow photograph with a wide mat can occupy more wall space than a larger unframed image.
Pick one clear alignment rule
Try a shared centerline, a level lower edge or a regular grid. You do not have to use every rule at once. A shared centerline can connect frames of different heights, while a grid emphasizes repeated sizes and spacing. Choose a rule you can explain in a sentence, then see whether the arrangement supports it.
Use a consistent gap as a starting point and adjust by eye. For example, two frames each 16 inches wide with a 2 inch gap have a total width of 34 inches. Three 12 inch frames with two 2 inch gaps occupy 40 inches. This arithmetic lets you rule out an arrangement that cannot fit before moving anything to the wall.
Test at full size
Lay the frames or paper outlines on the floor and photograph a few arrangements. Make full-size paper templates for the strongest option and compare them on the wall using a method suitable for the wall finish. Check the view from the places where you spend time, not just from directly in front.
Keep labels on the templates so each one matches its picture. If you change a frame or mat size, update the template too. The plan should describe the pieces you will actually display. A small sketch is useful for trying ideas; full-size outlines make spacing and scale easier to judge.
Keep the plan useful through installation
Record the group’s overall width and height, the gap you chose and the position of each outside frame. Separate this layout plan from the method used to attach each frame. Fixings and supports depend on the wall and the complete framed object, so follow the relevant product instructions or use a suitable professional.
Keep the drawing after the group is in place. It makes it easier to swap a picture, replace a frame or extend the arrangement without starting from memory. A gallery wall can evolve while retaining the spacing and relationships that made the first version work.