Ive been able to lucid dream since I was like 11. Though I haven't been bothered to do it in the last couple of years.
Like the above said, simply put you need to open up the gap between the subconscious and conscious through meditation. The easiest way to spot youv'e achieved this this is when all your prejudices dissapere in your mind or you appear to be talking with someone else, (although most prejudices you won't know you have so it might be a bit hard to detect). This is extremely difficult to achieve and can only be done the first few times while you are allmost asleep. Another way to breach the gap is by breaching the sub-conscious to conscious visual elements. Again this is achieved through meditation etc. A final way is through sound, although this is the most difficult and least productive so I wouldn't recommend even attempting it for a long time.
Eventually you can do some crazy things with months of practice. I can turn off my entire vision while im fully awake and instead see what my subconscious is thinking about. My eyes are wide open but all I see is hallucinations coming from my subconscious (((alot of sex, damn perverted subconscious >.>))). This can be quite a neausance taking it this far however as it can cause you some visual problems for a few days. Again this can be done with sound but its much harder. What I can't do while im fully awake though is breach the thinking part and listening to my subconscious, maybe ill attempt that one day but im not sure if its even possible.
Although my methods of doing these things are purly personal to me and may or may not work for other people, I could go into extensive detail on techniques if you want to PM or something. I dont want to write a 4 page essay here on how to lucid dream or any number of things.
Anyway Rowan. As an answer to you. Everything about this is designed for the subconscious to fire the information into your receptive senses and mind like it does while you are unconscious (which is where dreams come from). If you can achieve this while you are still conscious you are doing something the body doesn't want you to do but it is still possible. The point is you are not leaving consciousnes, but existing with the subconscious at the same time. I remember the first time I managed to achieve it and my body went on the fritz, I swear I allmost had a heart attack lol. It really didn't like me doing that for a few times after either.
And as a final point Kyra pointed out the 1 most important fact. It is something extremely difficult to understand and accomplish but must be achieved. You must not "think" about meditating or trying to see things or trying to hear your subconscious but you must also "listen" for it at the same time. The best way I can describe it is "knowing" what it is you are searching for but not "thinking" the words in your mind. Relaxing is idd a good way to explain it ^^
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