You have a very smart worker in your team but he is very careless? How to deal with him?

First i will advise him to take care of his work and tasks required and if he responeded to my advice and began to work efficiently and effectively i will give him an opportunity for training like soft skills course to be aware of time management , stress management and problem solving.

I actually had this problem with one of our community managers and it eventually worked out. All I had to do is talk to her and explain the growth potentials for her career if she would only be more focused and organized. And it worked.