This question is similar to asking how you arrive at decisions that must be made in the workplace. Keep in mind that no matter what type of job you may have you could easily find yourself in a situation in which you would need to make an important judgment call or decision. Even someone in an entry level position could find themselves in a situation where they would need to make an immediate decision. Your goal in answering this question should be to demonstrate that you have the ability to review the facts that are relevant to the situation and consider all of the choices or alternatives and then make a decision that is based upon the most appropriate action for that given situation.
When you form your answer to this type of question you should make sure that you discuss the way you would consider all of the resources that are available to you at the time as well as any constraints that might apply to the situation. This will show that you do not make hasty decisions and that you can be relied upon and trusted to make decisions that are wise and based on information available.
You may be able to easily relate your answer to a situation in which you have encountered in the past on a prior job. If your work experience is limited that may not be possible but you could still relate your answer to a situation in which you needed to make a decision on your own. Remember that your answer should show that you are able to work independently when the situation calls for it, which could very well happen no matter what type of industry in which you are involved.
This interview question should not be taken lightly as it is likely that you will encounter this question in an interview at some point. You should give thought and consideration to how you can relate this question to your prior experience so that you will be well prepared to answer the question if it is ever posed to you. This will help you to make the best impression possible on the future employer and also provide you with the best edge in terms of other candidates who may be interviewing for the same job.