What are the skill sets I will be required to know in order to write a good philosophy essay?

It is extremely important in philosophy, more so than other subjects, to demonstrate your ability to think critically and analyse arguments. The examiner will be looking for your ability to think, rather than your ability to just regurgitate information. So it is very important that you think reflectively about the issues. A good way of demonstrating that you have independent thought on the subject would be to come up with your own examples, to use throughout your essays instead of those in textbooks and other learning resources. Rather than just considering your own point of view, a good technique for insuring you have considered both sides of the argument would be to play the devils advocate. Making notes on what you personally think, but also how the other side of the argument would criticize.
Nevertheless, it is still important to ensure that you know the argument well and that your thoughts and arguments are clear. Try to insure that from the introduction of your essay to the conclusion you know what direction your argument is headed in. If your argument is not clear to you, it is going to be even more confusing for the examiner. So, overall I would say it is important that you use a clear concise structure, helping you to demonstrate your ability to argue and your knowledge on the subject matter.