How much is going on and how the different notes interactat the same time.
The tune or melody is the bit you would sing and is normally the bit of a song that you remember. It's in the foreground. The accompaniment is sounds in the background that sound good with the tune, but aren't what you focus on when you're listening.
The speed of the music. A fast tempo has more beats per minute than a slow tempo.
Loud/ quiet. Getting louder, getting quieter.
The type of music: Chiptune, EDM, Pop, Jazz, Soul, RnB, there's a lot of options!
Bear in mind classical music is divided into periods. If you want a classical sound, but can't find the specific type of classical sound you want, try looking up these periods: Medieval music, Renaissance music, Baroque music, Classical period music, Romantic period music, Modern classical music.
Basically, if you want the music to be interesting and attention grabbing, you want it in the foreground. If you want it to barely be noticed and be minimally distracting, it's background music.
The instruments used. You can mix and match!
If something is high pitched, then something small probably made the sound. If it is low pitched, something big probably made the sound. Boys and birds normally have higher pitched voices than grown men and bears.
When sounds happen, how long they last and how quick or slow those sounds are. Generally, a fast rhythm is exciting, a slow rhythm is relaxing.
Are there gaps between the sounds, or are they smoothly connected? Is it bouncy and spiky, or silky and smooth?
If there's gaps, it's called staccato.
If it's smooth, it's called legato.