Well, this is a tricky one.

Telling your subconscious mind to do something is exactly like talking to a mirror.

Go and try it. Stand in front of a mirror and say - You will have a Lucid Dream tonight.

Will it make any difference ? Exactly as someone pointed out - whatever you expect to happen deeply in your mind - that's exactly what will happen.

And, giving a strict order to a DC is also tricky. The question is - if you were that DC and you (as your waking consciousness) would give you an order - would you listen to yourself ? See, that's the tricky part. You would listen to yourself, but your subconscious mind is exactly what the name suggest - it is not CONSCIOUS. That means it cannot actually use any logic or something like that - all the logic comes from the outside world and from your consciousness. Hence the dream-logic is actually the logic of your subconscious mind - it actually is not logical at all, but flying on a rainbow unicorn makes perfect sense to your subconscious mind, because it has no logic on it's own until you program and insert some into it

You have to understand that your subconscious mind is like a Windows OS - and your conscious mind is a user. The windows has it's own logic - but all that logic has been programmed to it by the creators and by yourself when you customized your settings and so on. That's exactly what you need to do.

Also, everything you ask a DC - it's like you are asking yourself. However, at that time, you are in a dream, disconnected from the physical world completely - thus you are connected with your subconsciousness deeper than anytime else. That means - your conscious mind literally takes out the answer from your subconsciousness, and with the power of consciousness - it formulates an answer that you expect. However, your subconscious mind by itself is of no value - think of it as a mind of an animal. It acts exactly as it is trained to act and gives you exactly what you train it to give you over the time.

You have to program your mind - if every day you take 30 minutes and meditate about Lucid Dream, I guarantee you that after 25-30 days, you will start to have Lucid Dreams very frequently. This works with everything literally in life, if you make something a habit, it must, by law, give you the result you expect it to give you.