(Click to enlarge)
Step 1: Trace your pattern onto the tissue paper
Step 2: Pin it onto your felt. For my birdcage, I cut out the bird shape and stitched him on first, then embroidered the cage and details over it. Start stitching right through the paper and felt at the same time. Don't pull your stitches too tightly or they can tear the paper.
Step 3: When you're done embroidering, gently tear away the paper. This is the fun part! you'll see your embroidery revealed before your eyes. ;) You might need to use a needle or tweezers to pull loose bits out from under your stitches.
Step 4: Do whatever you want with your embroidery! I made a little pillow with mine. Easy as pie.
I hope this tip helps you out. It's made my embroidered felt projects a lot easier. :) This technique would also be perfect for other thick fabrics like velvet or terry cloth. Try it out!