And here's one I just made:
Spiky borders are pieced onto paper. Cut newsprint or paper in whatever width you want; for this example it was 4.5". The border will be sewn from left to right. I used strips that were a minimum of 2" wide - just made it easier.
Now the next strip is added. The strip HAS to meet up with the top end of the previous strip OR be to the left of it. See that bit of black fabric sticking out on the top right? You need to see that. Plus, the new strip has to meet the bottom of the previous one. Meet or be even further left. And notice how the new strip bumps up above the paper? You'll always need that.
After you've sewn the seam, make sure you've got a quarter inch seam allowance there, or at the very least have caught that spike in the seam by at least an 1/8".
Continue on that way. Trim excess, trim even (always with the piece opened up - do not cut off the tail of the fabric while right sides are still together).
This is how it looks for the up spikes. Notice I have the tail of the strip going up off the paper.
Be casual about it. If some of the spikes don't even spike, that's great. If they're all wonky and sort of different, then none of them are wrong. This test border I did for you isn't very wonky. It does take a while to get warmed up. Just keep practising.
This is what the back of the piece looks like. I tear out the paper a bit so that I can cut off excess fabric where I need/want to.
To make the borders longer, tape a new piece of newsprint on before you get to that bit and just keep sewing. You could also sew two individual units together, just be aware that the join won't look the same.