This will only work when napping, (Hence it's called Nap Induced Lucid Dream!) because night's sleep is way, way too deep for this to work, and even if you do get it to work, you probably won't remember it in the morning. Another time you can try it is if you wake up early in the morning, like after six hours of sleep, and then go back to sleep.
First, just get in a comfortable position that you are normally in when you are going to sleep. It doesn't matter what position, what ever feels the best. The main part is to control your thoughts. Do not let your thoughts drift of into some random thought like it usually does when you are falling asleep. Keep your mind on where you are and what you are want to do. You are in your bed, and you're about to go asleep very soon. Think about this and nothing else. If you start thinking of other stuff,
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Soon you will start feeling the weird sensation that you get when you are very close to falling asleep. You feel kinda dizzy and stuff.
As soon as it seems like you are about to fall asleep, start moving your hands or legs, just slightly. This is to test whether or not you are asleep. Just some very tiny twitches about every ten seconds, just don't do it too much, so you don't disturb yourself from falling to sleep. It takes no effort to move your body when dreaming so the difference should be very easy to notice.
When you start to notice that your limbs move very easily with just the power of will alone, congratulations, you're lucid dream has started. Now, enjoy your Nap Induced Lucid Dreams!