Prepare a poster board or heavy cardboard. Choose a size that will be big enough for your pictures. Select your Pictures, either from magazines, the Internet, your personal photos, color paper, any two dimensional mementos or even copies of family photos.

The surfaces should be free of dirt and grease; you might need to sand the surfaces in order to assure cleanliness. Cut around the part of the picture you want to include in the collage. Start gluing your pictures and Try different arrangements until you get one that looks just right.

You can use different kinds of mediums, for lightweight and flat materials (paper, canvas, etc.) use Acrylic using the fluid or the gel.
For heavy weight and 3-D materials (beads, rocks, etc.): Use Acrylic Gel Mediums.
Some papers are very absorbent, so if acrylic medium is absorbed into collage surface, allow medium to dry. Apply a second coat. The second coat will not be absorbed by the collaged surface. The acrylic medium to fully dry it takes for the Fluid Mediums 1-4 hours, gel mediums 24-72 hours, depending upon thickness of application
When you finish try to dry clear with a gloss finish.

Once you feel your collage is complete allow the collage to speak to you, for sure it might let you memorize beautiful events you experienced in the past, and at the same time it might become a source of decoration that makes your home elegant. As you can get several color copies or use your scanner and color printer to make copies. You can frame one, put magnets on the back, and hang it in your locker. You can make a smaller copy and cut and fold it around a plastic juice can for a pencil holder. You can slip one in the front of a 3-ring notebook. Cover a pencil box with your collage, and many other interesting and creative ideas.