If you dream of a sunny day, it means clarity. See things more clearly, see clearly where your steps are directed. If you dream of a cloudy or gray day, it means sadness or a possible loss.
If you dream of a particular day, look at the number of the day and remember it. It can be an important date in your life: a birthday, a wedding anniversary, the birth of your child.
To dream about a day of the past means that you should make more of your time and focus on your goals, rather than replaying your past.