When you are clear about your position, the other party understands specifically what you are asking. Many of us feel uncomfortable asking for something directly, especially if we do not have authority over the other person. However, think about your own experience and how refreshing it is when someone approaches you directly with what they need rather than tentatively approaching the subject. Courtesy does not weaken your position. Consider the following options:
(Bad) Can I ask a favor? If it’s not too much trouble, can you possibly do this report today?
(Good) Can you do this report today?
(Better) I need this report today, please.