Responding to Student Writing

Give assignments in ways calculated to elicit the kind of student writing you want:

Write out the assignment (in take-home form)
Identify its primary traits, and be sure to emphasize these in discussing the assignment with the students. Explain what you mean by each primary trait. [specific aspect(s) of content, organization, emphasis, definition of particular terms, review of the literature, whatever...]
Give process oriented assignments--tell students how to write what you're asking them to do.
Spend considerable time in class going over the assignment, explaining how to write it and what you're going to look for. Entertain student questions on this.
Be explicit about your grading criteria in advance.

Make exemplary models of professional and student writing available for students to refer to during their own writing.
Help make students aware of time management in planning, researching, writing assignments:

Optimum time of day/night to write. Optimum place.
Schedule research/writing time over period available to do it in--work backwards from due date to present. Be realistic.
Have students build in small rewards during the writing process to help themselves keep at the work.

Set aside a few minutes of class time at each meeting to discuss ways of handling the writing assignment and to entertain questions.
Don't become an editor of your students' writings, either of their drafts or their final papers.

Use a check sheet or some other response format that suits your taste and the assignment. Supplement that with computer-written comments, if possible.
Consider portfolio grading, especially of assignments with multiple drafts.
You don't have to put a number or letter grade on every assignment, or on every stage of every assignment.
Decide when not to comment--at all, or minimally. Particularly true of experimental or exploratory stages of writing.
Decide what to focus on in responding to a particular piece of writing--perhaps one or two of the primary traits you identified in the assignment.

Avoid response overkill--too many comments make it impossible for the student to sort out what's important.
And they're self-defeating; how can a student correct so many blunders all at once?
Better to pick a primary trait or two for each assignment; build on those in successive assignments as you escalate the complexity of the demands, and also your expectations of higher quality.