Select an image you want to paint on your wall. If the image has several colors, each color should be a separate stencil and all the stencils should have registration marks to line them up on the wall.
Tape the image onto a table with painter's tape. Place tracing paper over the image and tape tracing paper to the table.
Trace the outline of the image with a pencil. At each joint where the outline changes direction draw a line using a colored marker. For long lines make the colored marker cross line every 3 to 4 inches. Trace over each section between the marks using a marker the color that you want to paint for that portion of the stencil.
Look at each piece between the cross marks. If you cut out that section would you lose any detail? If there is a detail inside the area, add a bridge or two to keep the detail attached to the stencil. Check each section carefully.
Draw a circle with a cross through the center near the top of the paper and near the bottom. These are registration marks.
Place stencil plastic over the tracing paper and tape it down. Select one color and trace the outline and bridges of that color onto the stencil sheet. Add registration marks and label each sheet for the color of paint. Repeat this for each color.
Tape a stencil sheet with a marker outline onto a glass or wood surface. Heat up an electric stencil knife and trace the outline and bridges. The hot tip of the knife will melt the plastic, and the marker areas will be cut out leaving a stencil with bridges. The bridges should be about 1/4 inch thick across the image.