Printing presses in the past used to require an assistant to place all of the little metal letters in a row to print each line of text. They looked like little typewriter keys. Because they needed to print the right direction on the paper, the actual letter on the metal key was backward. This makes a p look like a q and vice versa. So the saying, “Mind your p’s and q’s.” means to pay close attention not to mix up the letters.

There are a few more explanations at the website below.

which stands for pints and quarts. in old england pub owners would yell this when patrons were getting rowdy.

Here is a site that explains it.

hence the saying.

It means dont get sick and dont drink too much