Slowly!
I have oft times found students in a rush to select a major believing that to enroll in college as "undecided" is not a good idea. Students also tend to compare where they are in their journey, to where their peers are so, if several have selected a major well, they must as well. We have all been there. We have all completed applications and have made decisions while looking over to the student beside us, wondering if we were just as far along in the process as they. Keep in mind that selecting a major does not need to be complete, until the spring of year two so you have ample time to make a decision.
But, if you would like to declare a major think about the things you are interested in. The things you enjoyed playing the most when you were very young. The classes you have loved and those you have run from.
Remember, you are not selecting a career. You may very well have an idea of what you would like to do post college graduation but you may not know either way, it is fine. When applying to college, you would do best to select an area of interest. For example, if you enjoy History, you can select Social Sciences as a major, taking classes those first two years that will help you to narrow down what it is you would like to do, how you would like to use a BA in the Social Sciences. It will be the classes you take while in college, that will help you define your career path. Starting out with a major which focuses on your area of interest, will allow you to investigate your options.
You can also sign onto the CollegeBoard and as part of the Quick Start program, take the My Road interest survey which will match your interests to careers and the education you will need to be in a position of entering the workforce in the careers you are matched with.
Good Luck!