You will need a pair of good scissors. The best scissors to use if you can get them are curved iris scissors. These are surgical scissors used for surgery on the iris of the eye. I got mine from a surgical supply house. The next best choice is a pair of curved cuticle scissors. Use your scissors only for decoupage, buy a second pair for the nails!
Find an image that you would like to use. It can be a piece of gift wrap, or a photocopy from a book, or printed from the web. If you are using printed images be sure to use good quality paper regular thickness paper and the highest image quality print that you can.
These cutting instructions are for right handers, lefties need to reverse it around. Hold the image in your left hand and the scissors in your right, make sure that the curve of the scissors are pointing toward your right also, you want the curves of the blades to be cutting away from your picture, not into it.
Let's assume you are using the koala picture here, it is the same one I used for the Australia Day ornament, and that you are going to stick him onto a glass bauble.
First you want to cut away all of the background, so that all you are left with is the koala.
The best areas to cut are along the natural lines in your image, these will become invisble when glued down and give the appearance of a flat, seamless image. For our koala we would cut along the lines indicated.
Now you have quite a floppy and flimsy piece of paper. When we glue him down, because of our cuts, little pieces of him will tuck in and overlap, this is exactly what we want to happen. We do, however, need to make sure that we glue him down so that the right bits are tucked away. For example, if we glued his head down first, then when it came time to do his chest that would overlap up over his nose, looking out of place. So identify which portion of the koala is the most background and start there, which is the chest area just under his nose.
Start with a small brush dab a little liquitex directly onto the glass ornament and then using your fingers to keep the area you don't want glued yet lifted, brush the first area into place. Now add a little more liquitex and smooth his face into position. Keep his arms lifted up, smooth his right leg down, then his tummy, then the arms and shoes. He should now be loosely held to the glass with Liquitex. Give him a good checking, ensuring that there are no gaps between the slits you have made in the paper and everything is in the correct order. Once you are satisfied apply firm pressure with a barely damp sponge over the top of the image, working a small section at a time. This is important to ensure that the image flattens and that all air bubbles are removed. Once he is smooth and fully secured set aside and allow to dry overnight.
The next day, using a clean, damp sponge, gently wipe over the top of him and clean the surrounding glass. You can now place another coat of Liquitex directly over the top of him as a final coat of sealant.