Your query is a sales tool, and good salespeople try to develop a rapport with their target. It can be helpful to show you’ve done your homework and that you’re not blasting indiscriminately. It can also set you apart from other writers querying—but only if it’s done meaningfully.

Here’s an example of a meaningful personalization: “The acknowledgments of The Superlative American mention you with praise, and B. Scott’s masterful work partly inspired my own novel.

If you personalize the query by saying, “I found you in Writer’s Market,” or “I see from your website that you’re seeking mystery,” and you add nothing else, that’s not terribly meaningful. Try to say something that can’t be repeated by another writer or used in another query.

I used to be a big advocate for personalizing the query letter and showing the agent you’d done your homework—that your letter wasn’t being sent to everyone listed in Writer’s Market. Today, I’m less enthusiastic about this because so many forms of personalization have become floppy and unmemorable. It is less about personalization and more about stating the obvious.

So, throwaway lines aren’t going to impress the agent. They will have seen them a million times before; they blend right into the background of the letter and have little or no effect on consideration of your work.

Here are a few ways to decide if personalization is merited for your query.

1. If the agent or editor has said publicly they do or don’t like personalized queries, follow their lead. This is simple: you’ll always be a better sales person when you’re aligning your pitch with the stated desires or submission guidelines of the recipient.
2. If you are stating the obvious to the agent, then try to make it charming to make it worth including. For instance: “I follow your blog and know you are currently looking for paranormal romances—without vampires or werewolves—and want to offer my novel for your consideration.” There’s a bit of a wink and a nod here, and it’s unlikely to be annoying to an agent who likely appreciates someone is paying close attention.
3. It’s great to open with a paragraph that acknowledges that you met the agent, conversed on social media, or had some other kind of interaction. When you mention this sort of thing, you mainly do it to spark their memory: “Oh, right, I remember this person from the San Francisco pitch event.” But it’s possible to go too far and evoke a coziness that isn’t really appropriate. For example: “We chatted briefly at the San Francisco Writers Conference reception, where I bought you a glass of merlot. I hope your two schnauzers didn’t miss you too much—I can’t bear to be away too long from mine. It must be hard to travel so much for your work.” Better: “We chatted briefly at the San Francisco Writers Conference reception about our schnauzers, and later I pitched you [such-and-such work]. I’m following up with the requested materials.” There aren’t any hard-and-fast rules as to what’s “too much,” but don’t try to affect an intimacy that doesn’t exist. Especially if you’ve never met the person in question, tread carefully—it’s easy to come off as creepy if you’ve been stalking someone online and found details they wouldn’t want or expect you to reference in a query. (“I see seven years ago that you went on a long vacation in Italy with your family. My novel is set in Italy…”)
4. A good strategy is to mention specific books represented or published, and it’s hard to find an agent or editor who doesn’t like it when you demonstrate knowledge of their clients or list. It’s ideal if you can reference such work in relation to your own, or express enthusiasm for it in some way that might connect it to the work you’re pitching. But it’s not mandatory. However, avoid buttering up or flattering the agent to a degree that makes you look silly or subservient. Talk about their list or their clients in a way that shows you have knowledge of the literary landscape or that appreciates their place in it. This works best if you can be specific, rather than saying something that could be lifted and placed into any query letter for any agent/editor. (“You’re the greatest and have the best clients!”)
5. In fact, that last bit is a good rule of thumb for any personalization: The more you could potentially lift that language and insert it in any query, regardless of who’s receiving it, the less meaningful it is.

The bare minimum: At the very least, address the agent by name. And spell the name correctly! Avoid first name only, since it may come off as too casual. Best convention is Dear [full name], e.g., Dear Jane Friedman.