The University of Washington Interdisciplinary Graduate Programs offers GRDSCH 200, an online course on preparing for graduate school studies. You can read more about it here: http://www.washington.edu/students/crscat/grad.html
To establish the seeds of success in graduate school, starting when you are an undergraduate student is important. Even if you don't plan to apply for graduate studies immediately after your undergraduate degree, there are still important steps to take if you wish to be successful down the line.
Setting yourself up for success: Things you can do while you’re an undergrad - Idealist - Includes considerations such as building relationships and making professional goals
Working after receiving your undergraduate degree can provide useful skills that will be applicable to graduate studies. Here are some websites that will help you consider the opportunities and challenges of bachelor's degree holders returning to school.