Welcome to the class!
Well when you get into the subconscious topic, ideas split here. I don't believe in a higher consciousness or a "subconscious" I believe in an unconscious. An amazing super computer that is semi random that works on schema, habit, and your own will. Your subconscious doesn't care if you get lucid, it doesn't think. It is a creature of habit, and it isnt used to the new things presented to it. You may have heard somewhere or seen a movie that implied that it doesn't want you to ld, or you might have been a little frightened when you got lucid. When you get frightened, it may connect your frightened mind more to the dream and cause it to go down hill. The same can happen if you are super happy. You need not be afraid of it any more than you are of putting a new software on your computer. The problem here is that you are continually changing the new software to be compatible with your computer, and your computer is different than everyone else's.
Being calm is a good thing in dreams, I recommend working on this first since it is the best way to remember goals that I have found. Just stop, calm, think about goals. Never worry about waking up, it will come some time, a thing is not beautiful because it lasts. Being excited doesn't wake you up (think about non lucids that you we're excited and didn't wake up...), but calm usually leads to awareness.
On the "changing things in the dream scene without changing scenes". I personally recommend learning to teleport as early as possible, but if you still want to do this, I would recommend changing small things and watching. For example:
I was once in a school. I looked to see what the school was teaching and had a huge banner saying "high school". I changed it to say "musician school" and all of the sudden all of the people were holding instruments, I changed it to say "dancing school" and all the people started dancing. I changed it to "Irish" and they all were wearing traditional Irish garb. I changed it to "Irish musician school" and they all were carrying bagpipes and going crazy. I am pretty sure I did more than that, but I also remember that I woke up laughing. Haha.
I don't like counting any dream control as easy or hard, but basic and advanced. Basic is if it doesn't go into anything crazy like sding, time dilation, or taking multiple dreams to finish a task. Basic is anything that can be done. Remember that when trying something "easy" like flying, that there is no difference between flying and teleporting. I leave you with the words from the matrix.
Dont try to bend the spoon. That is impossible.
If you know the next lines, that is great. If not, I recommend that you just rewatch the matrix. Write down that line and put it on the front of your dj. The most basics of control and the only way we can accomplish anything worthwhile in a dream is through creativity, and that quote, if you ask me, is a great take on what happens when we are creative.