Create a background. This can be as simple as a sheet of heavy paper, a wooden board painted in your favorite color or even a clean cardboard box. Choose a background material that is sturdy enough to support the layers of paper and Mod Podge that you will be adhering to it.
Choose the elements you wish to include in your collage. A predetermined theme will help to give your completed collage a unified look. There are unlimited numbers of themes, but a few possibilities are family, flowers, a favorite color or color scheme, sports, school events and weddings. You might include ticket stubs, pressed flowers, copies of vintage photos, decorative papers, fabric swatches, seashells, candy wrapper or any other ephemera that holds meaning for you.
Experiment with ways to lay out your collage elements. Move things around a few times. Add more items or take away something to see how the overall effect of the collage changes. When you have decided on a pleasing layout, you might find it helpful to write down a few notes or make a sketch so you will remember how you had the pieces arranged.
Cut out your collage elements with scissors, if necessary. For softer edges, tear them carefully with your fingers.
Brush a thin coat of Mod Podge onto the back of the first collage element with a small foam brush. Place it in the desired position in the background and smooth it out with your fingers. Continue in this manner, gluing each element one at a time until all the elements of your collage have been glued. Allow the glue to dry completely.
Add embellishments to your collage. For small pieces such as beads, buttons and shells, hold them with tweezers and dip the back of the object into the container of Mod Podge. Place the item gently onto the surface of the collage. Let the glue dry completely.
Coat the finished collage with a coat of Mod Podge to seal it. One variety of Mod Podge Hard Coat can be sanded after it is completely dry to give a glossy finish. Mod Podge Outdoor provides a finish for use on projects that will be displayed outside. Use multiple coats if desired, but allow each coat to dry completely before applying the next.