How do I keep my new hair color from fading too soon?

Tip1
Make sure you're using a shampoo created to protect and beautify color-treated hair.
Tip2

Make sure hair is SOAKING WET before applying shampoo and lather ONLY ONCE. Condition each and every time you wash your hair (also look for products made for color-treated hair). Also, ask your colorist to use a high quality anit-fade color like Joico's KPAK when retouching your roots.

Great proteins married to fabulous advanced dye system will keep hair looking its absolute best

Tip3
When I get my hair colored, the first thing my hair dresser tells me is to try not to wash it every day because the more often you wash, the more quickly it fades. Since I have somewhat oily hair, I almost can't get away without washing every day. So my solution (based on her recommendation) is to dampen a wash cloth, lather slightly with baby shampoo (use whatever brand you prefer) and just wash/rub at the roots. As long as you don't get your washcloth too soapy, you should be able to just rinse the soap off the washcloth and wipe your hair to rinse.
This works perfectly for me and it helps me to maintain my color for a bit longer.  There are also some dry shampoos out once again you can use on in between days.
Tip4
Needless to say, SUN FADES THE HAIR so cover up at the pool or when walking out to get some rays!