if yours haircolor was dark before, then dye it in a really light shade of blonde, then dye over the blonde the color you want. Light haircolors have better results when you wanna dye them qskdjmflqskdjfqmlsdkjg :D

just wait for a week bb
since I also dye my hair and I need to wait for a week until it become blend with my natural hair color
and also use a shampoo that for colored hair it make it become brighter and last longer with some vitamins too
well I hope this things help >.<