Here i will tell you what thoughts will have a small and big effect to the surroundings inside your dreams.
First of, the big pictures/thought are those which stay in your mind for a while and come back sometimes like things from movies or songs/music.
The second things are thoughts which come constantly or lets say scenarios which are built often in your head from nowhere because you like drama.
And the third things are small thoughts with not much attention to it, those which go immediatly to the „trash“ but they still are there and wont cause much trouble. These are mostly things which wont do much and could be seen as almost empty papers in the pile.
So shortly said, a mix of the second and third with a big scoop of the first are causing your surroundings in your dreams. BUT this is often as well not the case because you might watch a movie about flowers and end up in a massacre of giant insects which try to hunt you down! You just dont know on what your subconsciousness is fed on and thats why you should meditate or take a break for 40 minutes from all electronic devices before going to bed.
Calm your mind and learn to control your unconscious mind, than it will be all clear.
Wanna know more about lucid stuff ?
A story of a body piling beaver
Time traps inside Dreams!
Are otherworldly contacts dangerous ? heres the answer