Grading writing is not easy when compared to something like a grammar or vocab test. There is no right or wrong answer; it's all kinds of shades of grey. So how to do it in a way that is fair and appears this way to the students as well?
My solution is to use this
ESL Writing Grading Rubric, even though within reading the first 2 or 3 sentences of a 5-paragraph essay, I know what grade the student will get. I use it because it *appears* much fairer in the student's eyes and this will significantly cut down on the number of complaints you get about grading.
The other top trick I have to reduce the number of complaints is this: I tell the students that of course they are free to ask me to re-grade their essay. And, I will do my best to look at with fresh eyes. But, I will spend 3-4 times the amount of time I spent the first time around and get out my red pen and circle every single mistake they've made and I will most definitely not overlook anything. Of course, they might get a higher grade but it's also very possible to get a lower one. So consider carefully.
Mean? Yes, perhaps, but effective.