The basic idea - put two long pieces of fabric together with some stabilizer inbetween - serge or sew around the edges - then, drop the feed dogs on your sewing machine and go crazy with some free-motion embroidery.
If you already own a sewing machine and/or serger, this project can be completed for under $10 (the cost of the thread and stabilizer).
Step 1: Cut Fabric Into Strips
I use a mat with a rolling cutter and a ruler but you don't have to -- just cut two strips that are the same length. If you would like a multi-colored Franken-scarf, you can sew smaller strips of different colored t-shirts together to make two long strips that are approximately the same length.
Step 2: Add Stabilizer and Pin
Tear away stabilizer on Amazon.com.
Don't worry if your scarf seems stiff and unwearable at this point. Once you wash it once, the stabilizer will soften and become more like cotton batting in a quilt -- squooshy and comfy.
Step 3: Serge or Sew Around the Edges
If you just own a sewing machine, just sew a straight line around the edges of the scarf on your sewing machine. If you leave an inch or so border, when you wash it, the edges will curl up and look finished.
Step 4: Drop Your Feed Dogs
If you're not sure where your feed dogs are, consult your sewing machine manual. Failing that, check for a lever at the back of the machine.
Step 5: Insert Free-Motion Embroidery Foot
If you sew without a foot -- just be very careful to sew slowly and watch your fingers.
If you purchase a Free Motion Embroidery foot make sure you get the correct shank type for your machine. They come in Low Shank and Slant Shank.
Step 6: Go Crazy and Free-Motion Your Pants Off
Sometimes I sew back and forth in lines that look like tree bark. Sometimes I sew all over in big loopy circles. Sometimes I do both on the same scarf. If you look at what you've done and you don't think it looks so hot -- just sew some more over it. Use contrasting thread - or thread that matches your material.
Trust me; it all looks good.
Step 7: Wash It - Then, Admire Your Franken-scarf
Now you get to admire how awesome your new scarf is. And wear it somewhere. And have other people tell you how awesome it is. Remember to say, "thank you."