When my daughter was younger, say below four years old, distraction worked well. I'd pull out my trump card toys that she reservedly kept her attention on. These were usually interactive and stimulating toys that light up or make fun sounds. They would quickly grab her attention and buy me some time to catch a breath!
Now that she's older and more discerning, we play the 'calming jar' game which helps to visualise and slow down those big emotions. I let her decorate a see-through jar with stickers (her favourite activity) and we fill it with glitter or sequins. When she's upset, she shakes the jar, watching it intently as the shiny bits float down slowly. This somehow soothes her, giving me the chance to talk through her feelings and guide her through deep breathing as we patiently wait for the glitter to settle. It's a good teachable moment on regulating emotions, and she enjoys the ritual too!
Also, as a toddler, she went through a phase of being scared of the dark. I would tell her imaginative stories with a twinkle in my eye about magical creatures that live in our house. This fascinated her and quickly distracted her from the fears. Of course, a soft toy or two never hurt anyone, so those were always at hand too!