When you can post a picture do. Now, first and maybe most important, ducklings do best with the company of another duck so if you can manage to get another the same age yours will do better just because of the companionship. If that is not possible, then something like a stuffed duck (small) for her/him to cuddle up against. That and a lot of human interaction.
Now, go online to someplace like Metzer Farms and read their "cheat sheet" on the care of ducklings. They will need some additional heat in all likelihood (do you have any idea how old he/she is?). Prepare a brooding area for them with bedding, water and food. Bedding can be shavings (stay away from Cedar) but I use old towels when I am brooding ducklings. They are absorbent and can be easily removed when soiled and laundered and reused. Make sure they have water at all times!!! They must have water with their feed. They should be able to completely submerge their face in the water in order to clean out their nares (nostrils) but, when they are young, they should not be able to actually get in the water to swim. Until they are older they can not secrete the oils they need to be waterproof. I use a straight edged bowl about 2-3 inches deep with a rock in the middle so they can actually stand on the rock and not actually be in the water. For feed you can use chick starter if you are not able to get waterfowl starter feed. If you use chick starter start out with the crumbles and add niacin to it. Brewer's Yeast (available as a power in most health food stores) needs to be added to their feed for the first 10 weeks or so to assist in the development of nerves and bones.
Do this and interact with them as much as they will allow. Try to get a companion duckling for them and they should do really well.
