Speaking loosely, Composition is determining which notes to play. Orchestration is determining whose job it is to play them. When and how those notes that have already been chosen are played is a matter of EXPRESSION.  

Here are the fundamental parameters that dictate expression and feeling in music.  

1 - DYNAMICS
(crescendos, decrescendos, swells, accents, etc)

DYNAMICS with organic instruments is a combination of VOLUME and TIMBRE changes 

1b - PHRASING
(essentially, how dynamics play out over a certain melodic statement) 

2 - ARTICULATION
(the type or quality of the sound - staccato, sustain, pizzicato, vibrato, etc)

Some instruments have more or fewer ways that can make different sounds (articulation types). Pizzicato, etc. I'm not going to get into articulation use much in this course beyond because discussing how to use short and long articulations in dynamic ways and the bonus lesson on vibrato. 

3 - TEMPO 

(Timing Fluctuations - accelerando, ritardando, tempo rubato, fermata, etc.)

Any that affects the the speed of play will fall into this category. In this course I am going to address both macro-level timing fluctuations (basically, the ones you would find marked on a page of sheet music) and the micro-level timing fluctuations that make a performance feel authentic and human.