Answer: For a deeply shaded area, you might try an easy to grow groundcover such as Vinca minor which is evergreen and has blue flowers in the spring. Or, you could try some low maintenance, long lived, shade loving perennials such as hostas and ferns. (Some hostas are very colorful.) For additional color in summer you could try growing impatiens. This flower must be replanted every spring.
Before planting however I would suggest you run some basic soil tests to check fertility and pH. Use the test results to fertilize and/or add lime. Before planting you would also add organic matter such as compost to the soil. Loosen the soil down about ten inches before planting.
After planting, mulch between the plants with organic mulch. It should be two to three inches deep year round. This will help keep down weeds, reduce watering needs, and also help feed the soil slowly as it breaks down over time.
To establish new plants you will need to keep the soil evenly moist, like a wrung out sponge. It should not be sopping wet/saturated or dried out.
Your state extension should be able to help you with the soil testing and interpreting the results. They may also have suggestions as to plants to try based on a more detailed understanding of the planting site and your overall design goals.
I hope this helps you get started.
Q&A Library Searching Tips