How do you critically assess a theory?

To critically assess a theory in a philosophy paper, you need to do three core things. 1) Firstly, you need to clearly explain the theory (this is where you show off all the knowledge, facts and figures that you've learnt). 2) Secondly, you need to show the theory's weaknesses and strengths (this is where you demonstrate your critical judgement). 3) Thirdly, you need to give your own opinion, or judgement on the theory.
Now, points 2) and 3) might seem similar, which is what trips a lot of students up. However, they are subtly different. Point two 2) shouldn't actually involve too much new creative thinking. You should, before you go into the exam, know the general strengths and weaknesses of a theory. For example, you know that a weakness of Utilitarianism is that it could result in the 'slippery slope' argument, whereas a strength is that it doesn't rely on a God to make the system valid. There's an aspect of regurgitation here, where you can show off all the lovely strengths and weaknesses you've learnt. However, it is in point 3) where the fun and creative part of the essay happens! Here, you get to decide whether the strengths of the theory outweigh its weaknesses, or not. This bit is your opinion. You can conclude that the theory is rubbish because it's logic has been refuted, or that it's the best out of every theory because unlike others (give examples) it doesn't rely of the divine to interject and give a moral code.
And voila! If you do points 1), 2), and 3) you will have critically tested a theory!