It is impossible to give totally hard-and-fast indications about grading policies where paper-writing is concerned, because the act of writing a paper is creative. It is designed to develop your thoughts in unexpected directions, test them out, and produce conclusions. No one can predict every possible way of writing a paper, so no single grading policy can be imposed rigidly. The comments below are guidelines only.

Remember that your paper is trying to demonstrate that you have come to grips with the subject and that you are in control of the information at your disposal (including the bits you may think don't matter, like spelling). To establish all this, there are some things that every paper should contain. I have assigned them to various grade bands, to emphasize how they work together to build your paper, and how they affect your final grade. Let us assume that your paper is anyway worth 50 points. Now:

10 pts
Grammar and vocabulary. Plain language. Past tense. Clear and direct sentence structure. Use of correct words for purpose. No malapropisms. If in doubt, look it up. Language is your first and most familiar logical process. It is how you label, organize and communicate your thoughts. If you are not in command of this basic logical process, you cannot be in command of what you are using it for.

4 pts
Successful understanding and following of ALL instructions
If in doubt, consult your professor or a writing tutor
3 pts
Good organization of your paper
Get paper-writing notes, if you need them
3 pts
Good presentation
Type or word-process your work, wide margins, double-line spacing (single for paper plans, clear line between sections), clean paper, illustrations on paper the same size as your text, diagrams done with ruler and compasses or stencil - a good general appearance

6 pts
General accuracy of factual content
Spelling, names, dates, events, quotations, references, acknowledgements, etc - do not invent "facts" because you think they ought to be true, or because they help prove your point. If you have to do this, you know already that your paper is no good!
4 pts
Adequate range of aspects considered, representative range of examples, completeness of sentences, ideas, arguments and discussions. Use of topic sentences and summary statements

3 pts
Catching the implications of the assignment
For example, the topic is likely to be fairly narrowly focussed, but it fits into the broader framework of the course itself. Think about how that works. What is the professor trying to make you think about? Try work that understanding into your answer
3 pts
Applying information, reasoning, speculating, demonstrating your points
Working things out in relation to established or partly established facts, using suitable language to convey logic, deduction, doubt or possibility. Showing why something you said is true - i.e. giving examples, quotations, evidence and references as relevant
4 pts
Going into dialog with the assignment
Supporting, developing or challenging the premise or thesis of the assignment. Presenting your own ideas, hypotheses, or understanding in contrast to or in dialog with the class and with published authorities.

3 pts
Catching the implications about how the topic relates to the present day with its very different values and social structures
Note if the topic demonstrates the introduction of values and ideas which we take for granted today, or which we think are important; note if the topic demonstrates the rejection of values and ideas we no longer approve of or believe; note if the topic demonstrates a partial step towards our own society - try and work some of this into your answer without stretching the point too far. You need a very light touch for this bit.
3 pts
Demonstrating a superlative degree of understanding, a unique and illuminating approach, or mind bending brilliance
3 pts
Judgement call
For everything that falls outside these guidelines

Obviously, it is not enough merely to do these things. You need to do them successfully and you need to do them well. Also obviously, if you have an A band quality of understanding the question, but your organization, presentation and accuracy are out - you won't get an A. Each grade is also about having got the ones before it right. It is hard to get an A: we normally expect less than 10% of any class to achieve one. Be proud of a B.

In the end, what you have to keep in mind is that papers in Art History deal mainly with non-factual material. Non-factual material is slippery stuff, so it has to be handled carefully. Your competence has to be proved in every possible way, as outlined above, so that your reader trusts your judgement about the rest.

If you need them, get the notes on:

Paper preparation (the research end)

Paper writing (organization to best effect)

Paper Presentation Requirements (to give yourself the edge)

Note taking (the course contains unique material - you won't be able to read up on it all)