It's been two years since my first BP, and sadly I had to sell her, but I've learned a ton since then.
I didn't make the same mistakes most newbies do, since I had cared for these snakes at the zoo and had done a TON of research, but let's see...

Used carpet for substrate
Picked out a rather undersized little snake
Fed in separate container
Fed hoppers for WAY too long
Used a rheostat for a long time
Used stick on thermometers

Tanks are NOT mistakes BTW...but they can be used badly. I didn't know at first about covering the top, or the back and sides.

But the whole point of sites like this is to learn...and keep learning.