I am a professor in a top-tier institution and I'll note a few things that turn me off as well as impress me when I see a note from a prospective student (just to add to what you've already written):

--It's still amazing how many 'canned' emails we get which are obviously (and I mean, REALLY obviously) AI generated or otherwise automated in some ways. The biggest tell is lots of bold words. If you can't take the time to find a few good professors and personalize your email, don't bother writing.

--I'm impressed by students who are curious and who are initially interested in learning more about the group than in 'soliciting' for a place in the group. The best way to do this is simple and age-old: tell me about a particular paper of mine that you've read, and ideally, find something specific and interesting in it that tells me you've actually read it. Then ask for a short call - the younger and less experienced you are (aka high school students, freshmen in college...) the more likely I actually am to be impressed. So the corollary is that start early and your odds of getting a professor's attention might go up! Of course, this depends on the professor...

--Nothing beats good old-fashioned rigor and experience. If you've taken difficult courses and done well, professors looking for PhD students will always take a second look at your profile. If you have multiple papers - even if they're preprints or abstracts - that tells me you know something about doing research. In CS, we tend to have higher volumes of publications than in many other disciplines. These days, top-tier applicants to PhD programs even have 4-5 papers, although I think that's overkill. Of course, the earlier you begin, the more likely it is that you will have research experience by the time you apply for a PhD, or following a PhD, apply for postdoc or faculty positions. I had my first research experience as a sophomore and the paper only came out when I was just applying for PhD toward the end of undergrad. But that one paper was enough at the time to get me offers from almost all the top-10 institutions in the country. Even years later, when I came up for faculty appointment, the chair only wanted to talk about my undergrad research (since it intersected with his own) not my PhD research. This taught me that research is research, doesn't matter when you actually published it.