"Add a video to your hero." A video can work, but on most pages it delays the headline, auto-plays into an annoyance, and adds weight that kills mobile load time. Use a video only if it makes the promise more concrete than text can, and never let it block the first paint.
"Use social proof everywhere." Social proof that is generic, unattributed, or repeated in five places stops being proof and starts being noise. One specific, named testimonial placed at the decision point outperforms a wall of anonymous five-star ratings.
"Remove all navigation." Removing the nav is correct for a true landing page receiving paid traffic. But if your page also receives organic or direct traffic, stripping all navigation can frustrate visitors who arrived with a different intent. The practice applies to dedicated campaign pages, not to every page on your site.
"Always use a long-form page." Length should follow the complexity of the ask. A page offering a free PDF does not need 3,000 words. A page selling a $5,000 service might. The rule is: the page should be exactly long enough to answer every objection a visitor has before they act, and not one section longer.