A simple and effective way to start warming up:
Pick one note (if you're a flutist, B in the staff is quite nice for this exercise).
Hold the instrument with as little tension as possible. Maybe even with just one hand if you can, letting the other arm relax at your side.
Focus on moving your air freely and finding optimal resonance. Don't try too hard.
Stay with this note as long as you need until you feel the resonance and vibration and notice warmth in the sound.
Try relaxing your knees, bending one at a time or shifting your weight side to side. Can you keep the resonance and ease of playing while you do this?
As long as you can maintain the quality of air movement, try walking around your space, making sure none of your joints are locked and your movements are fluid.
Now carry this ease of air and movement as well as the beautiful quality of sound you have created through any long tone exercise you like, beginning on the note you started with.