I assume basic SQL knowledge. At the start of most procedures, I state the reason for the procedure - why it exists in the first place. I then add comments for blocks of code explaining what it does, but just a description of the step. It's usually 1 or 2 lines long. Personally, I can't stand comments for every line, but that's just my preference.

There are times when more comments for a block of code are warranted to explain something that's little more complicated, but (as Grant said above) this is a matter of opinion. It all goes back to readability and maintainability of what you write. You may be the one maintaining it, but then again you might not be.