One of the easiest ways to smooth out a vocal line in a song so that all notes work together as a unit, is to sing it through on a single vowel.
The “oo” vowel is especially good for this, when it’s round and spacious. And all you have to do is simply pour the sound through that shape as you connect each note to the next.
This strategy is very good for lots of things: note-reading, checking intonation, legato, breath management, resonance, phrasing, and on and on.
But what if you’re singing staccato? It still works. Just use your diaphragm action to articulate – don’t articulate from the throat. Imitate a Santa Claus laugh while touching the soft area just beneath your sternum. That point is what I call “the button,” because that’s what you use to activate the breath for singing. Use this for staccato singing on a single vowel.
Or, you can put a consonant in front of your vowel: “doo,” “loo,” “noo,” “too,” and so on. Different consonants will give you different effects, depending on what aspect of the music you’re practicing: “noo” will draw attention to resonance in the mask, while “doo” can help make intonation more precise. Experiment and see what works best in your situation.
Ultimately, what a single vowel should give you in your singing practice is unity – throughout the phrase, throughout your range, throughout your physical instrument. It’s one way of reducing degrees of freedom to isolate any challenges you face in singing a vocal line. As you sing on a single vowel, there should be no sensation of a break or kink in the phrase, even if there are rests.
From here, you can graduate to a different challenge: maintaining unity in the vocal line while singing on the words. You’ve dug the trench; now sow the seeds. Just simply drop the syllables on the path of the vowel you shaped in the previous exercise. The whole phrase becomes one gesture of breath and sound.
Or, take an intermediate step and sing only on the vowels of your text. Do the vowels flow into each other smoothly? Does the phrase remain a unity? Do you lose placement or feel an abrupt change when shifting from vowel to vowel? Record yourself doing this, so you can hear the difference it makes.
Add another element: dynamics, expression, or tempo. And keep going, step by step, to create the whole. Any new thing you bring to the table from here should only add to the unity you’ve created with the single vowel, and not take anything away. Even if the music shows changes or multiple facets in its final product, it will remain a unity – if that’s where you started in the first place.