Design the letter and other decorations.
Copy the letter into the color paper.
Place the figures as you wish the card would look like.
Add glue to the acetate sheet.
Spread the glue in all the sheet.
Pass the design into the sheet with glue and let dry, it'll take like 6 or 7 hours or less if you expose it to the some daylight.
Now it's dry, add more glue.
Pour some glue. When it'll dry this extra glue will make a translucent effect
Once you have it like this you have 2 options: 1) let it dry; 2) add glitter
Add glitter in some specific places. I diced to put some in the balloons to make an effect of lighting. Then let dry.
To Have better results with glitter you could add it when the final cap of glue has dried.