Professionalism
As a school leaver, there's a chance that you've never really experienced being in a professional environment other than school. For this reason, employers often find younger job applicants a bit too laid back. When applying for jobs, it's important that you show that you have a professional approach to work and that you understand the importance of maintaining high standards.
And this goes for job interviews too.
If you have a job interview, make the effort to look professional and dress the way that employees of that company would dress.
Organisation
Being organised is a great life skill in general but particularly useful in the workplace. In a lot of jobs, you'll be responsible for managing your own workload, which means being organised so that you meet deadlines. They key to having good organisational skills is to have processes in place. In every job, there are always certain tasks that you'll need to do over and over again and having an effective process in place can help you get things done quicker and more effectively.