How should I structure a philosophy essay?

The most important thing is to have an argument running through your whole paper and to be very clear throughout what the overall conclusion you are aiming at is. A good idea, especially in shorter papers, is to respond directly to an argument in the literature that you have covered. In this case your essay structure might look something like this:
Introduction ( 1 paragraph)Exposition of an argument (2-3 paragraphs)Your response to the argument (2-3 paragraphs)Consider a counterpoint and respond to this counterpoint (1-2 paragraphs)Conclusion (1 paragraph)
In any case, you should be able to articulate your argument clearly in a series of premises that entail a conclusion and ensure that you have discussed and defended these premises at some point in your paper.