I am not a professional, I am just an at home hair Do It Yourselfer :) So please take this as what worked for me and only,ONLY try this if you have experience with what works on your hair.

First I started out with Platinum almost White hair that has been dyed from a box this shade for years. I am however naturally a dirty blonde so my roots were being touched up every 3 weeks. I use to have long thick dirty blonde/dark blonde hair forever, until I got the bleach blonde urge.

I wanted to give my hair a rest and dye it back to it's original color and just let it be for hopefully the next few months.Here is what worked for me going from platinum blonde to dark blonde or light brown at home.(This is the process to get light brown or dark blonde, I fell in love with my hair much darker when I dyed it so I kept the dark auburn hair and I will tell you how to what I used to get this too) This is also a helpful tutorial if you have dyed your hair from blonde to brown and it turned green/khaki/grey and you want HELP!Just start this process like you hadn't dyed it and this will save your tresses.

1.Condition your hair for a week leading up to this process you don't want your hair to break off.

2.If you live near a Sally Beauty or Beauty Supply go buy Protein Pack for your hair and use it a day or 2 before you plan on dyeing it.

3.Going darker won't kill your hair as much as going lighter will but it still isn't filling your hair with sunshine and sprinkles.

4.Going from blonde to dark blonde sounds easy peasy, but it is a 2 step process.

5.You must first go red to add the brassy red tones back to your hair that you have worked for years to get rid of with all your might.

6.I bought a dark auburn hair dye, if you aren't wanting dark brown hair please buy a Fire Engine red hair dye almost orange because you cannot lift dark brown hair with a box without bleaching it. So for light brown hair or dark blonde buy BRIGHT red,fiery red,orangey red hair dye for your first step because you can make it darker so don't worry. 

I left the Auburn dye on my hair for 40-45minutes starting with my ends because they are more damaged and get less oils. I completely saturated my ends and then worked my way up, I also added a little water to the empty bottle of dye and rewet my ends after about 10 minutes. The ends of my hair don't like to take color because they are a little more dry than the rest of my hair.

(You want it to be this shade to get the brassy tone back into your hair preferably without the highlights but its okay it will give your hair depth.

7.Then pick out a box of hair dye that your desired shade,my original shade was Medium Blonde 8 by Clairol Nice and Easy Color Blend Foam