Here’s some general tips for providing feedback on general composition:
Early in the semester, refuse to grade assignments that reflect sub-par effort. Often, we instinctively do the opposite - if I give this student a low but passing grade, they won't get irrevocably discouraged. But even a low but passing grade will encourage some students to think they should just "get by" in your course, instead of adopting a growth mindset: I can get better at this. And then you'll be struggling to grade and give feedback for weak work for the rest of the semester.
Build one or more low-stakes writing assignments early in the course, so students learn your expectations by doing work and getting feedback.
Concentrate on a few big things, rather than drench their submission with markup. If the work was exemplary you might only have grammatical corrections to suggest. But if a student's work is really below standard, pick a few essential things. For example, this might be a faulty argument, or some structural problems, that they should work on improving. This keeps students from getting overwhelmed, or struggling with what is more or less important.
Try to offer actionable advice: this could be improved if you did this or that specific thing. (For example, could the student have included more evidence to support a particular claim? Could the student better organize their paragraphs?) Depending on the nature of the assignment, this could point to how they could revise a draft, or do a better job on a similar task in the future.
Try to find something good in their work, and point it out. Seeing this, a student might garner a little confidence in themselves and your wish to help them, and be more likely to employ your constructive criticism in future.
Provide opportunities for students to earn a few additional points by responding to feedback. This may be an entire revised draft, but it need not be. Perhaps they can simply elaborate on an area where their argument was vague or weak, or they were mistaken about something. (This can be useful for exams, too.) This need not be text; a student could create a video note or audio clip in response to feedback.