If there are too many dark spots the cauliflower needs to be thrown away.
Whenever I cook cauliflower, I first boil some water and add a teaspoon of salt or vinegar to it. Then add the cauliflower whole or the florets let it remain for 2 min. then drain the water. Now the cauliflower is fresh and clean. Has adequate moisture and any bugs etc are removed.
Use it as you want in any dish.
It's a funny thing about life, if you refuse to accept anything but the best, you very often get it. - W. S. Maugham