Well, it's sort of like in The Matrix where Morpheus says "Don't think you are, know you are". However, I've found that this always seems to happen more during negative type situations.

An example would be when I would have a dream as a child where I did something I was afraid I would get in trouble for. I would go to my room and try to hide, but I still had the thought that my dad was about to come in and I'd be in trouble. Sure enough, it would happen!

Also, maybe you're not waiting long enough for the dream to carry out your orders. Even with my experience, I still sometimes have to wait a little bit to be able to do impossible things. It's like the dream has some kind of slow processing issues or something!

But instead of putting the focus on your power within the dream to say "This or that should happen", maybe you could try going up to someone in the dream and getting them to make things happen for you. This can work because we often percieve the surroundings and characters in the dream to actually be more powerful or have more influence over the dreamworld than we do (even though we know it's a dream).

I like how Hidden mentioned trying less direct forms of dream control. Also, I've found that if I try to control too much about the dream, it only ends up being stupid, and not happening the way I want it to.

I also agree with starting small too. There's plenty of time to work your way up. Rome wasn't built in a day