||On the micro-level: If all elements in the music you're composing are at the same volume, there will be not depth. It is a good idea to let something take lead, and have other sound elements that are in the background.
On the macro-level: If your song is the same volume all along, there will be no climax or development. Make sure your music rises and falls in intensity. Contrast is what it's all about.
||Use the entire stereo image, if you're making stereo. Don't just leave everything panned in the middle. Spreading it out make it easier to distinguish each sound element. Be careful not to pan stuff with bass too much. And leave the main theme or main vocal in the middle.
|Bass / low freq.
||Treble / high freq.
||Make sure each instrument has its own frequency area. Especially in the bass area, things easily clutter up and get difficult to recognize. A good balance between bass, mids and highs is important for something to appear pleasing to the ear.
|Melodic / tonal / harmonic
||Disharmonic / atonal / noise
||This is genre-dependant to some extend, but if possible, try to utilize the entire spectrum between having both clean tones (flutes, voices, string instruments and generally sinus-like sounds) and stuff that isn't any pitch at all (drums, percussion, noise). And everything in-between is good too.
||Are all your instruments playing something fast? Then add some slow stuff to add a dimension. If all instruments are playing slow stuff, it gets boring. There should be both slow, medium and fast things happening.
||Check all the various instruments. Are they all short? That's not good. If they're all long, that's not good either. There should be both.
|Legato (no gaps between each note)
||Staccato (gaps between notes)
||This is affected by genre- and instrument to a large extend, but it could still be relevant to consider if any variation could be achieved on this level. Should there be pauses between the notes or not?
|Close and dry
||Lots of reverb
||This axis starts at the front of people's faces and moves back and away. Not adding any reverb can makes sounds appear close to the listener. Do not add the same amount of reverb to all instruments, because that will produce a soundstage with no depth. Some things should be dry, others should be reverbed to different degrees. Different types of reverb can be used in the same piece of music to achieve an even bigger and more complex soundscape.
||This trick is much the same as the one above. Effected sounds tend to be further away from the listener than un-effected sounds. Both should be present for the mix to be as versatile as possible.
|Clean and pure
||For those music genres that use distorted sounds, my advice is: Very distorted sounds place themselves differently in the mix than clean sounds. Having both distorted and undistorted sounds will give the biggest sound universe.
|Straight on the beat
||Off-beat (e.g odd 16ths or odd 8ths)
||Only using the "straight" 4ths or 8ths or 16ths will give a rhythm that is too predictable and easy to understand it becomes. More emphasis on the odd parts of the beat will make it more "funky", abstract or even chaotic and impossible to understand. Pop music uses the straight beats a lot - jazz does not.
||There are two major reasons to make music repetitive: It becomes easier to predict what is coming, which makes it easier for listener to comprehend, like pop music. Repetition can even make the mind go into a light trance, which is what techno and african music uses a lot. Too repetitive music, on the contrary, becomes boring. Consider where on this axis you should be.