Proper Spark Plug alignment?

So I took out the old spark plugs and put in new ones. And on the first ignition of my car a lot of smoke came out of the exhaust pipe. I waited a little bit and re-ignited the engine and the smoke was gone. What does this mean? Did I do something wrong while putting in the new ones? I was told to never tighten to plugs once inside the engine, so I didn't. But also it's necessary to properly align them? How?