What do you see when you close your eyes?
At first, you see nothing, blackness. Yet, if you continue to observe, you begin to "see" something else. Areas of light begin to appear, swirling and changing shape. The images appear in varying shades of gray, with some areas being very bright or appearing as flecks or slivers of light. These are called phosphenes, which, translated from the original Latin, means "light show". Phosphenes are created by random electrical stimulation of the brain's visual cortex, that is, your mind's eye. You are, literally, looking at your own brain's activity. And as long as you observe, you do so in a state of no thought. However, if you continue to observe, another part of your mind goes into action.
One of the brains main functions is to gather and analyze sensory data. And even though your eyes are closed, the brain still gets input from the visual cortex. It tries to correlate what it is seeing into something it can name, in the same way that you might try to find, to recognize a thing when you look at clouds. Once this has happened, the brain generates a cascade of useless thought. The vision of the phosphenes becomes blurry and fades, replaced by irrelevant mind movies.
So then, the key is to recognize when this happens and quickly switch your attention back to the phosphenes, to the state of no thought.
If you were in an unfamiliar darkened room, it might take awhile to find out where the light switch is. However, the more times that you turn the light on, the faster and easier it will be to find the light switch. So, find the switch that brings you back in to presence. Learn to recognize the change from no thought to thought. Don't judge yourself for not being able to maintain the mindful state for very long. The more times you find the switch, the faster it will become second nature. And, the ability to stay in that state will increase automatically.
Make sure to not only be aware of the light, but also the darkness, the nothingness from which the light arises and recedes into. For there could be no light without the darkness, and no darkness without the light.
If you can maintain this practice, one day you will achieve something wondrous. You will be able to attain the state of mindfulness...with your eyes wide open.