There is no right or wrong way to make a collage. There are, however, techniques that will help create a more balanced result and that you can use or not at your discretion.
Making your main image the largest image in the collage ensures that it doesn’t have to fight for attention against the other images. Use repeated elements, colors, and shapes to unite the collage. You can do this by using multiple images all the same size, by repeating colors or shapes, or by using the same image more than once. When determining multiples, use 1, 3, or 5 of an item rather than 2, 4, or 6 for a more pleasing presentation. I did this with the buttons across the bottom of the final image (see Figure 10).
Figure 10 The final image has three buttons in the bottom-right corner and features many repeated colors and shapes.
Keep in mind the Rule of Thirds, which suggests you place an imaginary Tic-Tac-Toe grid over the image and align items of interest along the lines or place them where the lines intersect. This avoids placing objects dead center in the image, which is less visually interesting.
Place objects over the edge of the image rather than completely inside its boundaries. For example, make a flower disappear over the edge of the collage for a more dynamic feel. Position objects that suggest movement in a particular direction (such as cars, planes, people, and signs) so they face into the image—not off the edge. When you look at an image, your eye follows the direction of movement; if that direction is off the edge of the picture, that’s where you will look.
Where possible, choose and arrange elements on the collage so that they appear to share the same light source.
After you start making collages you will find ideas in everything around you. Magazine advertisements provide rich inspiration for new layouts and when you’re out taking photographs, look for signs, textures, and other elements to use in your next collage.