Reflect on your current position in college. If you are just beginning, you will have more liberty to plan out your courses to include widely divergent double majors, such as English and math. If you are getting towards the end of your college career, you are probably locked into a particular area. As a math major, for example, you might be able to add physics on top, but you might not be able to add English without delaying your graduation.
See exactly what you need to graduate in your current major. Most colleges will have the requirements spelled out pretty clearly, so you will be able to see how many distribution credits and which upper level classes you require.
Compare your requirements to the time you want to stay in college. Figure out how long it would take you to graduate with your chosen major in your current program of study. How much extra time do you have? How many extra hours do you have to take classes each semester?
Reflect on your reasons for wanting to double major. Are you an analytical student who wants a second humanities major as a way to engage your creative side? Do you want a second major in a field close to your major to make you a stronger job candidate? Come up with a few choices for a second major and reflect on their advantages and disadvantages.
See how much extra work your various double major choices will take. What classes will be already out of the way with each? What new prerequisites will you need to take? What upper level classes and projects will be required of you? Will you be able to graduate on time and, if not, will this be a problem?
Chose the best major. Pick one that will enrich your academic studies while not taking longer than you can afford to take.
Meet with a counselor. Discuss the choice you made and what it will mean for your academic program. Sometimes, counselors can waive certain requirements, or at least give you good advice.