Articulation - a mixture of slides, accents, short and long notes and more
Ornamentation - a mixture of decorative features such as vibrato, riffs or licks, melismatic runs, accidentals, trills or ulutations, shouts and more
Dynamic control - going from loud to soft and vice versa, sudden loud moments, sudden soft moments, whispers and more
Pitch control - slides instead of going up or down note-by-note, fall-offs, a mixture of talking with singing, singing high using falsetto outside of one's expected vocal range, leaps in pitch, ascending or descending in steps, arpeggios, ad-libbing, imitation, improvisation and more
Rhythm - use of syncopation, triplets, straight rhythms, dotted rhythms, long note values and short values and more
There is much more that vocalists do to create their style and ultimately communicate emotion in their performance. Listen to the vocals carefully in any piece of music to see if you can spot all of the details that contribute. Much of the above will be present.
Breathing exercises and techniques
Enunciation and pronunciation. To enunciate is to sound clearly. To pronounce is to sound the word correctly
Projection
Dynamic control
Articulation such as staccato, legato, slides (portamento), fall-offs, accents, slurs and much more
Pitch control
Pitch flexibility and agility
Falsetto voice
Riffs and runs
Relative pitch training
There's much more that students can explore when it comes to vocals.
In music at Wrotham School students almost exclusively are encouraged to use one online resource to help with all of the above and almost all things that vocalists would have to cover. This is the YouTube channel Jacobs Vocal Academy. This resource avoids talking and 'fodder' and simply has a wealth of exercises that students can use daily.