When mixing it is importing to keep in mind that mixing is all about context. Something will sound loud if played in context with something that is quiet. Likewise, an element in the mix will sound wide if played in context with something that sounds narrow. With this in mind make use of panning and effects to position elements for width and depth.
For example, you might be mixing a track which which contains a lot of synthesizer sounds and you have been given the stereo outputs of all of these synths. If you pan each stereo output hard left and hard right, then ultimately you end up with everything sounding wide – as a result everything sounds narrow. This has been commonly referred to as “big mono”. What you could try instead is taking either the left or right channel and then adding your own panning and effects to position the element within the sound stage. By careful placement and keeping context in mind you can achieve a wide sounding mix.