When you are about to warm up – whether it’s for practice, rehearsing, or performing – start by making sounds with your voice. It doesn’t have to be a song, or an orderly scale, or an appropriate engagement of a particular register, timbre, muscle group, words, style, or anything! Just make vocal sound in a way that is pleasant for you. Play, just to get started.
As your voice starts to turn on, explore a little. Swoop up high and dip down low. Try some louder and softer sounds. Try some long steady sounds contrasted with quickly moving patterns. Go from a favorite vowel to others. Just play, and notice.
In the first two minutes of sound-making, don’t rush to bring in structure to solve problems. Scale patterns, rhythms, and vowels can be worked into focused patterns for the voice to respond to LATER in the warmup. Your voice’s tendencies may be similar most days, but eventually there will be a new issue to deal with. An open, exploratory beginning will help you discover any new issues more quickly. This discovery would be hindered by plowing through the same warmup routine from start to finish every day.
If there are long-term technical goals like range extension or dynamic control, those exercises should come AFTER your warmup. They should not be the warmup itself. The very beginning of your warmup must always belong to you alone. The first sounds you make in a session should not contain shoulds, musts, caution, criticism, or complexity. Just get moving. Play, listen, play a little more, listen. THEN start work. If you want to use warmup exercises from a teacher or other expert, consider delaying them until after your first two minutes of “free me time”.