I would find out which agents have blogs or websites, and I would tailor my manuscript to their preferences.
I’m not published, but I would advise against that. Depending on the work being submitted.
For novella or longer fiction, this is not practical. Such works aren’t produced overnight.
In my limited experience, this has not really been a factor.
Tailoring THE QUERY, though, that’s been far more significant. We as writers are not just trying to impress agents or publishers. The agents, the publishers, are trying to decide if this is a work they are best suited to sell.
Agents and publishers turned down Harry Potter, a series that’s turned JK Rowling into a near-billionaire. And some of them don’t regret that. It wasn’t the right work for them.
It’s not just about selling to agents. They also have to believe that they can sell it. Sometimes it’s a great work, just not for them.