I haven't been able to open all chakras simultaneously yet. I suppose I have blockages in the lower ones. However, having been able to activate the upper ones on some level at the same time, maybe I can offer you guys some help if you're a beginner.
When you meditate, do so with the idea that you are not simply your body. You are not just a part of the universal cosmic mind, but in a sense you ARE the universal mind, and so is everyone and everything else. Expand your awareness to everything, every rock, every blade of grass. Expand your awareness out into the universe. You are everything and everything is you.
Erase your fear and your preconceptions. silence your mind and focus on peace and calm and love for everything and everyone because we are all one, whether living on this planet or on others. Every race, whether reptilian, mammal, amphibian, or whatever, is made of the same light, has the same spirit.
You may expect to feel a swelling of energy in your heart area. you may feel vibrations or pressure in your head and/or twitching between and just above your eyes. you may feel your throat open up. Your body may shudder or tritch involuntarily. tears may flow down your cheeks for no reason. You may notice flashes of light with your eyes shut. Your spine may begin to move involuntarily in a spiral motion.
This is as much as I have ever experienced. I don't know what is beyond this or how to get there, but I do know that I always feel better afterwards.