AwakeTooLong is correct. And:
Not one chakra is more important than any other. They are simply a part of your energetic anatomy - like a finger or an internal organ. All the "chakra-opening" hype is simply that - hype. Go ahead and do all the visualization exercises you want - you may get some fleeting results - most likely you will just practice your visualization skills.
Like any part of your anatomy, your energetic anatomy (including your chakras) is best cared for like you care for your physical body: a good diet, exercise, plenty of sleep, a positive outlook, and emotional fluidity. Visialize all you like - if you don't make supportive lifestlye choices, your energy/qi will suffer.