Personally, every time before I have my hair dyed, I will prep my hair basing on the below several processes.
About a week before my hair color appoinment, I will give my hair a clarifying treatment.
Sometimes my hair is damaged to some extent, so a regular protein treatment is necessary for my hair for a few weeks prior to my hair color appointment.
A few days before your appointment, a deep conditioning treatment is also is essential for restoring moisture and balancing the pH of my hair.
Usually, the color I have my hair dyed tends to last longer and shiny because of what I have done.