A specific, benefit-led headline
Your headline is the single most important element on the landing page. Most newsletter landing page headlines fail for the same reason: they describe the newsletter instead of the benefit the reader receives. "My weekly newsletter on marketing" describes you. "One practical marketing insight, every Tuesday — for founders who are tired of vague advice" describes the reader's outcome.
Write the headline from the reader's perspective: what will their life or work look like after reading your newsletter?