The black rubber things are the coil packs, their positioning is not important, it probably wouldn't hurt to remove the front connectors and give them a quick spray with some contact cleaner just in case there is any debris in there causing a poor connection , did you use the correct type and heat range of plug ?, I am not familiar with the NGK plugs as most of us are running Densos.
You can also do the spring stretch mod if you are experiencing rough idling, stuttering etc, a quick search within the forum, or google should find it for you.
If you are experiencing rough idle after fitting new plugs, I would retrace my steps before just throwing a bottle of injector cleaner in there, rough idle can be attributed to spark plug issues (check the gaps etc), as well as possible air leaks from removing / reinstalling your IC.
Nearly all men can stand adversity. But if you want to test a man's character - give him power.
Abraham Lincoln