Whenever your supervisor starts talking to you about work, immediately grab a note pad and a pen and start taking notes. You never know quite how detailed/substantive the instructions will be until you have finished receiving them! As soon as you have finished receiving the instructions, another task may come up and by the time that is complete, you may have forgotten important details from the first set of instructions.
Whenever you go to meet someone else and there is a chance they are going to give you instructions, bring a pad and pen with you just in case.
Make sure you fully understand your instructions before starting the relevant work. This includes understanding the deadline, how long the work is likely to take, how detailed the finish product needs to be, who the intended audience is and how the work should be presented.
Consider reiterating/summarising the instructions back to your supervisor once you have received them, just to be sure (and to let them know) that you fully understand them. This will also give your supervisor the chance to assess whether they have in fact given you instructions that are clear, accurate and complete.