The colour of your lips primarily depends on your complexion, but fair people can also develop dark lips if they smoke excessively or consume too much of tea or coffee.
Having one or two cups of tea or coffee in a day does not matter, but consuming too much of it should be avoided.
If you are a smoker, quit and apply Vaseline on your lips regularly to prevent
dryness.
Protect your lips from the sun. Wear lip balm with SPF 30. It makes them soft too.
Hydration of lips is very important. Eat lots of vegetables, fruits and fluids.
Superficial exfoliation of the lips can be also done. One can use salicylic acid based lip balms.
Don’t get permanent tattoos on lips.