DO!
Pray about it :) This seems like the typical response for a lot of things BUT...prayer is powerful and God can help clear your mind and help you to accurately focus on what you are evaluating.
DON'T!
Grade when you are tired. Or if you get tired when you're grading take a break! Switch up the order of how you grade. Instead of always starting alphabetically, switch up the order and grade from the bottom up. We are human and as we get to the end of our grades we sometimes grade easier.
DO!
Check that what you are grading is authentic work that demonstrates the skills you are working on in class. Don't give kids busy work :) I'm totally guilty of this!
DON'T!
Grade based off of your "memory." Participation grades are always a pain for me, but I'm working on taking an extra 30 seconds at the end of each class to mark how the students participated during that class and using that data for grades.