Colorful veggies (beets, carrots) are great to spiralize, but they can easily stain your spiralizer. Make sure you wash your spiralizer immediately after use.
Zucchini noodles (Courgetti) and any other vegetables full of water can easily get soggy. Place them in a colander and sprinkle with salt. They will release most of their water content within 10-15 minutes, then dry them with a paper towel.
Spiralize your veggies ahead of time during the weekend, and place them in an airtight container in the fridge. This will speed up your dinner prep time in the evenings, during the week.
Pick the most symmetrical veggies you can find. As much as I love ugly looking vegetables, the straighter the veggie is, the easier will be to spiralize it.