There is no simple recipe to follow, but here is some advice that tends to produce better papers (and therefore higher grades):
I do not know whether there are right answers to some of the questions we are considering this term; I suspect that there are, but that itself is yet a further a philosophical question! But I am sure that quite sure that if they have right answers, they are subtle, controversial even among reasonable, informed thinkers, and very hard to find (especially in the space of a single course in philosophy).
Fortunately, I do not grade your work by determining on whether you have made claims or presented arguments that I happen to think are the uniquely correct ones. (Although remember that there are some things that you might say in a philosophy paper that would clearly be false (e.g., "Pascal says that we should not believe in God.").) Rather, you will be graded on the quality of your reasoning, the care you take in thinking things through, and the clarity of your expression. I have no doubts that it is possible to grade objectively along these criteria; you would be amazed at how closely philosophy instructors agree over what is a strong or a weak paper by these lights.
And sure, everyone is entitled to his or her own opinions and beliefs. But what does that mean? I suppose we mean by this that no one can throw you in jail or fine you for the views that you happen to hold. It likely also means that we should respect your independence and integrity as a thinker and give what you have to say a fair and respectful hearing. But it certainly doesn't mean that your (or my) views cannot be wrong, or that every argument is as good as any other. Even if there are no unique correct answers to philosophical questions, it does not follow from that there aren't any wrong answers. Not every view is equally entitled--not every claim or argument is just as good as another. Some are better, some are worse. It's our job as thinkers to try to sort them out.
I evaluate papers by assigning letter grades. If your grade for a paper consists of two grades separated by a slash (e.g., B+/B), that means that your grade lies on the boundary between the two.
Most of the grades that students earn in my classes are in the A- to C+ range. For most students, earning an A- or an A will require a fair bit of careful work and revision. Students who receive grades of a C+ or below almost always turn out to have ignored the advice I present in this guide. In particular, they turn out not to have started early or to have shown other people their work in order to get feedback on it.
No. That would unfairly punish students who happened to be in with an excellent class and unfairly reward students who happened to be in a weaker class. Instead, I rely on my experience from grading thousands of student papers to fit the quality of your performance into a general letter grade scheme for an undergraduate course at this level. So if everyone were to write an excellent paper, everyone would receive an A. But if everyone were to write a disastrously bad paper, everyone would receive an F.