I procrastinate and am unorganized to a fault. How do I improve?

I am a full time college student and a full time retail salesperson. I am having a very difficult time managing my studies around work and what little social life I do have. School is the most important to me, but seems to be the hardest for me to do well at. I put off my assignments until the last minute, because I know I can pull it off. But when I do this I get stressed out and don't do the project as well as I know I am capable of doing. I have tried limiting my social outings to spend more time doing homework, but without a social life I feel like I am letting down my friends. I need a better way to go about things and maybe a mentor to guide me. Any suggestions?