Expand Your Course Work
Don't limit yourself—take as many different math and science classes as you can, and augment these with carefully chosen classes that will improve your speaking and writing skills. Classes might include English literature, business management, accounting, oral communication, scientific writing, etc. If you're interested in teaching, take some courses in the Department of Education.
Grab Research Opportunities
Get involved in research as early as possible. You will learn many valuable skills, even if you do research in an area that is not the one you are planning on pursuing. This will make you a more attractive candidate when applying for graduate schools. Research experience is still valuable if you choose to go directly into the workforce or another field, since you are learning so many other skills like how to solve real problems, how to work with deadlines, and how to improvise.
Know Your Professors
Get to know your professors so that you have people who can write strong, knowledgeable reference letters for you (as well as let you know when there are opportunities available.) You'll need good letters of reference no matter where you decide to go after your undergraduate work.
Network with Physics Students
Join or start a chapter of Society of Physics Students to develop leadership skills. Advancing in any career takes leadership and it makes sense to start developing those skills now. You will also become more visible in the physics community, and that can help you when looking for employment.
Most physics majors say that the most influential factor in their decision to study physics was a great high school teacher. You could be that teacher.
Apply to Graduate School
Many physics majors choose to attend graduate school, which is generally free for graduate students who teach or do research.
The information above was provided by the American Physical Society.
For more information, visit: http://www.aps.org/careers/physicists/undergraduate.cfm