I am a licensed cosmotologist, and here are my tips:
~What you see on the box is not always what you will get!!!
The reason for this, is because everyone has a different starting color. A blonde, a light brunette, a redhead, and a darker brunette can all buy "medium auburn" hair color, and they will all end up with a different shade. This is because boxed haircolor uses the same developer for everyone-which is why haircolor boxes recommend that you pick a shade close to your natural color already. If these 4 women all came into the salon and wanted the exact same shade, I would mix it differently for each of them to achieve the same color. So basically, if you are a blonde, don't attempt dying your hair black, if you are a brunette, don't attempt to go Paris Hilton blonde. It will screw up, and you will end up in the salon anyway.

A boxed haircolor usually uses 20 volume developer-so it is meant to only change the shade 1-2 levels-not a great deal lighter or darker. This is how women who try to dye their hair blonde get the "orange" or shades of orange.
~Highlights and color are different things. Lightening the hair and highlights strip/bleach color OUT of the hair shaft, and color deposits color IN the shaft. Use shampoos and conditioners meant for what you have done to it.
Keep in mind that once your hair has been highlighted, those strands of hair will take color differently than the "virgin" strands will.
~Red is the hardest color to keep, and the hardest to get rid of. People who dye their hair red have the hardest time keeping the red vibrant-because it tends to fade quickly. Don't wash it every day, use shampoos made to extend the red, etc. Red hair is also the hardest to remove-so if you don't like the red, and try to dye brown over it later, etc. the red will still have the tendency to peek through in the sun.
~Don't apply the color all over, if you dye the hair regularly and use the same shade. If you do your hair every month, don't apply it all over. Do the roots only, and put it on the rest of the hair for the last 5 minutes ONLY!!!! If you put it on all over, it is too much damage, and you also will get the dreaded "rainbow" hair shaft. You know, where the brunette goes from medium brown at the roots, dark brown in the middle, and fried, almost black ends...or the blonde goes from medium blonde at the roots, down to the ashy white "cotton" looking fried, damaged, last couple inches of hair.
~The basic hair color ingredients are the same in cheaper to more expensive colors, but the harshness and the conditioning agents are what is different. The more expensive colors are usually fortified with more vitamins, conditioners, and things that lessen the damage.
~Think about the things that will need to change when you change your haircolor. Your clothing and makeup shades will need updating. For instance, if you have a "cool" red, like the burgandy red tones, you can usually wear rose and pink shades-however, if you have a true red, like strawberry blonde, copper, or other warm reds (like natural redheads have) pink is pretty much a no-no-especially hot pink. CLASH big time.

Pink gloss might look great on a blonde, but a redhead would need more red, brown, or coral/orangey shades in lips, nails, etc. ( I am a redhead and stay with earthy makeup colors, and lots of black and green in my clothing.)
~Don't do too much. I don't recommend highlighting your hair one month, dying it red the next, and then brown the month after that. It is too damaging on the hair. Short hair can take it, because you cut it off before there is too much-but longer hair can't.