EQ (equalization) is a professional version of the tone controls on your stereo. It’s the most basic and simple tool in the audio toolbox, but it causes a lot of confusion and is often abused.  EQ is powerful and versatile, but you can easily destroy a mix with it.  There’s no trick though.  Like a lot of things in life, all you do is adjust to taste.  It’s a little like cooking, too much salt and you’re going out to dinner.  It’s worth the time and effort it takes to develop a sense of taste.