How can I nurse this plant back to health?

What kind of plant? Too much water will kill a plant as well as too little. Water schedule depends on the type of plant. Some do better getting drowned once a week and dry out, others need just a little every day, cacti need just a little every month. They also need light and leaves to make them grow. Try to get some information from a gardening book that shows the type of plant and how to treat them.