Lets write a original song!
Find your motive/melody: Write a balanced 4-bar phrase in the theme.
Create varied rhythms in repetitive passages.
Think of ways to create and vary texture throughout your piece.
Vary the dynamics, e.g. crescendo, diminuendo.
Include phrasing marks, legato, staccato.
Have a clear beginning and end.
Make sure your parts are playable.
Complete your musical notation, and remember to add time signature and bar lines.