If you want to graduate early, the first order of business is to visit your school's testing center. If you possess the knowledge to test out of some of the general education requirements, you don't need to waste credit hours. You won't necessarily receive credits for testing out of courses, but you will receive exemptions from requirements for subject matters of which you prove you have a comprehensive understanding. This clears a path for you to hone in on your major requirements sooner rather than later.
If a school is semester-based, then a full load for undergraduate students generally is five classes or 15 credits. In a quarters-based system, a full load is four classes worth 16 credits. If you meet your institute's grade point average (GPA) requirements for overloading--3.5 in most schools but sometimes 3.0--you can register for a sixth class at the end of the primary registration period each term. While it may not seem as if taking an extra three or four credits per term will make a difference other than an extra load of homework, you could overload every term beginning in your freshman year's second semester and earn up to 15 extra semester credits by the end of your junior year. That equals a complete semester of work, which would give you the freedom to graduate 1/2 year early.
An alternative to overloading each term is to take summer courses. You can do that in one of two ways: Finish your general education requirements during summer at a community college from which your four-year school accepts credit transfers, or take general education requirements and major requirements at your four-year school during summer. Generally, summer sessions are divided into four-week and eight-week sessions. So you can take up to a full semester's worth of credits during one summer. If you spend two summers taking full loads, you can graduate one full year early.
A lot of students must work their way through school. With internship programs on the rise everywhere, though, work can help you graduate early. You may find internships relevant to your major through your school's career center, allowing you to earn internships that give you real-world experience and credits.