After trying to figure out why my photos all had a small black semi-circle at the bottom, I learned the hard way: you have to remove your lens hood when you’re using a flash.
When you don’t, as you can easily see, the flash is blocked from lighting the bottom of your frame, and you end up with not a black semi-circle, but rather, a shadow.
It only took about a hundred pictures before I finally deciphered this simple bit. In the process, I removed my polarizer, changed my focus, and even tried the lens hood upside down.
I also figured out that while shooting in manual mode is fun, it’s almost impossible to quickly go from well lit to medium lit to dark without a lot of practice. I shot a small event (my sister’s wedding shower) as a favor, and it took about 10 minutes for me to surrender and shoot entirely in auto.