Warm-ups are a singer's best friend. They should be treated with reverence and exploration.
But don't go about them 'religiously' - trying to find something you found before. Your objective is to find something new (and hopefully exciting) every time. Go for the pleasure of it.
You start with a sound. Any sound, something that feels right for that very moment. You notice how it sounds, how it feels, how it resonantes, and you work with what you find - not what you expected....
Then you start modifying that sound - changing your mouth position, changing the pitch, changing the vowel, adding a consonant, repeating short syllables, etc etc. Notice how this new sound feels, modify it, and go again. Eventually, you'll then end up in a very different place to where you started. Then you go back, either to your start note, or to some other sound you like along the way, and see how that sound develops the second time round.
And so on!