I was reading a few articles on the internet about lucid dreaming control. After a lot of reading, and using a few ideas from various sources, I think that maybe one way to control dreams is to cause a chain reaction of events. For example, if you want to find your pet cat in the dream you could do this:

1. Find some pot plants in your garden and put them in the road

2. Wait for the milkman to come

3. Let the milkman swerve off the road in attempts to avoid the objects in the way, and crash.

4. The milk will leak over the road

5. Various cats will be attracted to the milk, including your cat

6. You can pick your cat up. He / she is now in your possession.

Rather than force an idea in a dream, or directly request something to happen, set the scene up so something "invariably" occurs. Like a row of dominoes.
Think of it like time travel. If you go back in time and kill your parents, you aren't going to be born. Your birth is the result of certain circumstances.