Plan ahead, starting on Day 1. Figure out what classes you need to take and when, taking into careful consideration any pre-requisites, especially for your major.
Test out of college courses. If you can get out of taking even one course, you are ahead of the game.
Declare your major early and stick with it. The sooner you declare your major, the easier it will be to get signed into closed classes in that department. Also, changing your major mid-way through your college career can easily push things back by an entire semester and even a whole year.
Work straight through the summer. Yes, a break is nice and may aid in your overall sanity, but if timeliness is important to you, than take a deep breathe and push through it.
Take courses through a community college. First make sure that the courses are transferrable by checking with your advisor and/or the department chair of that course's department. Get it in writing that the credits are transferrable. Community college courses are typically a little less demanding and are more flexible with the "working man's" schedule.
Stay healthy. Exercise, eat right and don't go on weekend benders that leave you miserable and unable to get your work done. Illnesses and injuries can set you back from completing important coursework, studying, passing exams and making presentations, all of which can result in you having to re-take the course.