Ezekiel had some good/interesting ideas for reality checks. I often plug my nose and try to breathe and that one often works for me.

As for changing your physical body, let's see... If you wanted to be a dog, you would have to visualize the dog: on all fours, tail, head and protruding jaws, ears. Get a feel for what each part feels like individually. Then add them all together, one at a time. I think that if you just kept at the visualization, thinking about the feelings, you would soon find yourself more like the object you desire to be. I don't know how difficult it would be to maintain it, but I have changed to other things in my non-lucid dreams and recall how it feels.

As for controlling someone else... well, they are just an extension of you, so it shouldn't be too hard. Rather than jumping in someone's head, I'd recommend walking up behind them and into them. Then feel the difference between their self and yours and proceed to control them. The biggest thing is keeping in mind that what you want them to do, they will do.

As for spinning, I have used this, though often unawares. I'd say the biggest use for it is if you are changing something in your dream. You start spinning in place, and when you stop you will be in the air, or in another room, or whatever you want. Again, you just have to know that it will happen. Some people use spinning to keep them lucid, but I think there are other more useful techniques, such as rubbing your hands together or against some object in the dream.

Welcome to DV and I hope this helped.

-Amé