Fail fast, often and early. Building the stamina to trial and error different concepts is crucial, and you need to be ready to part with ideas and work if they don't ultimately serve the overall story or purpose.
Check your work with fresh eyes as often as you can, including getting feedback from others. Remember to take mini-breaks every now and then, and you can be surprised at all the new things you notice before and after.
Lastly note-taking and sketchbooks are invaluable! Whether it's writing down why a particular film moved you, sketching the strange way someone on the train sits, or trying to analyse why you didn't enjoy a show - noting little memories somewhere can be incredibly useful when you create your own things later on. Do try to come up with an organised system, otherwise you can end up having to deal with hundreds of post-it notes later (totally not what I did...).