Is it a good idea to pretend that you are about to perform something impossible during waking life, just so you get a feel for how you should think when you eventually dream about it?
For example, I sometimes stand on the floor and try to jump into the air, just to see what it feels like and how I should direct my thoughts.
The training I do is basically all about becoming comfortable with the feeling.
Don’t think that is necessary, you just have to believe that everything is possible within your dreams.
Yes, but it’s one thing to rationally know that you are able to do anything, and another thing to actually feel that self-confidence.
And I believe it could be a good idea to prepare and work on that discouraging feeling so you can get used to the idea that you are suddenly able to break the laws of physics.
I mean, if I were to try flying in a lucid dream (I haven’t tried yet 
), then I would probably just feel like I’m gonna fall down on the floor or something, which is exactly the way I feel in real life.
So it could become easier to get used to that attempt if you practice that idea in real life, and try to develop a confident attitude to it.
I often use physical life experiences for my Lucid dreams and normal dreams. I think you should keep enjoying yourself because a good idea is what is good for YOU! Do you think acting like this will help you? If yes keep doing it, build on it. … if not find something else that you can relate with.
This is just my point of view but I believe everything is connect so in waking state if you “pretend” to do things im sure it will benefit you in the dream world.