When you have the food all ready to go, call its destination to find out if someone is home to receive, and also ask if it's a good time to come and visit. Sometimes, when someone brings dinner they assume it's fine if they hang around and chat for an hour or two.
Sometimes it is fine, and sometimes, after a long day of doctor's appointments, physical therapy, and a never-ending string of phone calls, we just want to eat dinner and get in bed. In most cases people will be happy to tell you if it's okay to come in, or if they'd rather you just dropped it off and visited some other time. Personally, I love the people who bring us wonderful meals, give us a quick hug each, and head right back out. We get to eat while the food is still hot, and later we can call and have a lengthy chat about how tasty everything was, and how much we appreciated it.