HELP! putting my ideas down

Im a high school senior and im lookin to go to art school…one problem i still seem to be having is taking thoughts from my head and putting them on paper…I have an idea of what I want each piece to come out like but I have a hard time putting it down…I do great when I have something in front of me that im drawing but I just cant pull stuff from my head…pleaseee help me out with this let me know what I can do to fix this! thanks

go here and get this video. I think it will help you out. also, look around this forum more, you’ll find other good recommendations for books/video/etc.