But I saw what happened. Googling Safire's rules, the "helpful" top result via Google quoted a source that misquoted Safire, which I'm guessing is how it made it into your comment. So no worries.
Good catch, though the fix I don't think is quite right. "Proofread carefully to see if you [have left/are leaving] words out" probably should've been what I wrote. I invite a much more competent writer to fact-check me.
"Proofread carefully to see if you [leave] words out." I believe is grammatically correct but a bit nonsensical as I'm no longer in the act of writing words when I'm proofreading. But again, I'm also possibly just embarrassing myself at this point.
> Remember to [preserve the full] infinitive.
> [Always use] the [active] voice.
> [Always] put statements in the [positive] form.
> Verbs have to agree with their subjects. (nobody9999 corrected this one already - was "has" in place of "have")
> Proofread carefully to see if you [leave] words out.
For those not in on the joke. Not sure if this would be how Safire would correct it, but I made an effort.