Say something good about the content of students' writing before saying anything else. Hands down, that's the most important thing. This is their soul on the page. Be sincere; you don't neeed to go gooey over everything they produce. But do rummage for and celebrate what they've done well.
This fits hand in glove with what we have learned through our study of Routman's work. This type of encouragement and celebration will produce students who see themseles as writers with meaningful messages. They will be more invested in making those corrections that will make the meaning all the more clear and appealing.