I'll try to be specific and use terms in carnatic music to describe each aspect
- Each Raaga provides key phrases which are set forth by the notes which are allowed in the raaga.
Aarohanam: notes(swaram) that can be played ascending
Avarohanam: notes that can be played descending.
A list of scales which are common is provided here along with audio:
- Signature verses: Signature verses bring out the quality of raaga(bhaava). There are certain notes which are given emphasis even though the aarohanam and avarhonam are the same for some raagas (refer list above)
Along with the notes allowed in the raaga, the style dictates certain notes should not occur together.
- Improvisation of a raaga requires a structure which gives its quality. This is often referred to as Manodharama.
Again, there are aspects which are specific to raaga, on how the aalapana(opera style improvisation) should start or end, which notes are emphasised, and which notes are less likely vs more likely.
Other than aalapana, Tanam (repetition), and Niraval (melodic transformations of a verse) are popular.
All of these styles provide a framework for a musician to expand, based on her abilities.