Fittonia prefers bright, indirect light. Lower light can cause it to lose some of its vibrant color and growth will slow. Too much light can burn the leaves.
Fittonia loves water and to be consistently moist, but not soggy. Water thoroughly when the top 50% of soil is dry. If you let your Fittonia dry out too much, it will let you know with limp leaves. Not to worry! After a thorough watering, the leaves should soon perk up.