Boy, did I make a lot of mistakes in setting up this cloth! Thankfully, none of them are affecting the quality of the cloth. They're just costing me a lot of time to fix.
Here are the results of one big mistake. Notice how the back shed is kind of a mess? That's because I had somehow twisted a bunch of the threads around each other when I was threading the harnesses.
To fix it, I had to untangle them after every bobbin until I reached a "cut line" in my garment pattern. Then, I cut the offending threads, carefully untwisted them, rethreaded and resleyed them, and stuck them to a piece of tape.
When I carefully resumed weaving, I found that I had successfully fixed the problem. See? A nice, clean shed.
Whew! Now I can make cloth at a reasonable rate. And that's what I'm going to do for the rest of the day.