The main sounds and ideas that you present in a track are by far the most important for the success of that track. But the ear candy background elements provide that professional polish that allow the main elements to shine through in the best way possible.
These effects can come anywhere from foley to effects samples.
There is one effect, however, that ties a track together with the use of the sounds that you already have in the track.
In this screencast, I'll show you how to create reverb tail effects for a more interesting and dynamic track.