A cover letter has one job the CV can't do: explain the connection between you and this specific role in a voice. Most letters waste that by restating the CV in flatter language. The reader already has the CV. Tell them what it doesn't say.
Open with the point, not a windup
"I am writing to express my interest in the position of..." tells the reader nothing they didn't already know from the subject line. Worse, it spends the most-read sentence on a formality. Open with the actual reason you're a fit, in a sentence that could only have been written for this job.
Something like: "You're hiring a content lead because the blog has volume but no through-line; that's the exact problem I spent two years fixing at my last company." That sentence shows you read the posting, understood the underlying need, and have a relevant claim. Three things, one sentence, no windup.
Make the middle about them, then you
The body is two short paragraphs, not five. The first connects a real need in the role to specific evidence from your experience. Not "I have strong communication skills" but the situation, what you did, what happened. The second can address something the CV raises but doesn't resolve: a career change, a gap, a pivot. This is the part the CV genuinely can't carry, so this is where the letter earns its place.
Write like you'd explain it to a smart colleague over coffee, not like a legal filing. Hiring managers read dozens of these. The one that sounds like a person saying something true stands out against a stack that sounds like a template with the company name swapped in.
Cut every sentence that could go in any letter
Run this test on each line: could this exact sentence appear in a letter for a completely different job? If yes, it's filler. "I am a hardworking team player passionate about excellence" passes for any role at any company, which means it does no work for this one. Specificity is the entire game. A detail about their product, their problem, or your concrete result is worth more than three sentences of adjectives.
The closing is a request, not a thank-you
End by stating what you want clearly: a conversation about the role. "I'd welcome the chance to talk through how I'd approach the first ninety days" is a closing with a forward motion. "Thank you for considering my application" is polite and forgettable. You can be both polite and direct; pick the version that gives the reader an action.
A note on length and effort
Under one page. Realistically, around 250 to 350 words. A long cover letter doesn't read as thorough; it reads as someone who didn't edit. If you're applying to many roles, the honest move isn't a generic letter sent everywhere. It's a tight template where the opening and the middle paragraph are genuinely rewritten per job, since those are the only parts anyone reads closely anyway. The same content discipline that makes a good CV work applies here: say the specific thing, cut the rest.
The letter that works isn't the most polished one. It's the one where the reader finishes the first paragraph and thinks, this person actually understood what we need. Get that far and the rest is easy.