If you have a grading rubric, don't keep it a secret from your students. Rubrics are an excellent way to let student know exactly what you want them to learn. In my 5 years of using rubrics in college teaching at a highly selective college I have never had the problem that giving the rubric to students meant everyone all did well on the assignment.

Giving out the grading rubric ahead of time does not make the assignment easier. It does make it clear just how hard the assignment is.

Every time I grade using a rubric, I find problems with it. Sometimes an item is to vague or too unclear. Sometimes I forget to include a dimension that seems crucial given the papers I now see. Sometimes there are simple misprints. I forgive myself for being human, and then try to figure out how to change it for the next time around. I recommend this rather than agonizing over how to fix things for that class. If the students got the rubric ahead of time, they knew what they were aiming at and justice is well enough served for the moment.

I have on occasion removed an item from the rubric because it seemed everyone was "getting it" and there was no need to mention it and if felt obvious. Then, I would find in the next term that very few people did the thing that was now not obvious since it was not on the grading rubric. Students only know what you want when you put it on the rubric. If you don't put it on the rubric, you don't care about it, at least for this performance.

The example rubrics we link to above are all for papers in a class. But rubrics can work for class presentations, debates, even group discussions and "class participation."