ideal would be no bubbles and just a bit of steam vapor coming off the top. There is quite a bit of error to this though. Here are a few things that I have done with success:
Let it get to a boil and then turn it down to low and let it sit.
Let it simmer with some little bubbles the whole time.
Turn it really low then get impatient and turn it to medium temp, then to ease the anxiety of waiting for the pot to get hot, I did 25 bong hits. I fell asleep for a few hours and woke up and said "SHIT I left it on to hot". I raced out there and turned the heat down, but most of the water had boiled out and it was toasting the weed on top that was now dry. I just added water let it simmer on low for a few hours and then strained it. While I do not recommend this, the butter was more of a sleepy high, but it worked.
Long story short: hot with steam and no bubbles or a few bubbles but its not a huge deal if you fuck up some.
