Understand how much the child knows before beginning to teach him. For example, if you are teaching the child how to read, understand how advanced their comprehension level is. This is important so you won't re-teach what the child already knows as it may confuse him.
Use visual aids when describing what you are teaching. If you are teaching the child how to write, show examples of letters. If you are teaching her words, then provide a picture of what the word is.
Target the problem. After teaching the child for some time, you will begin to understand where the learning disability lies. Every child is unique -- it may be that the child has trouble concentrating for extended periods of time, therefore, you must teach her with breaks in between. It may be that the child has problems with phonetics when trying to read and may not understand how to sound out a word. The better understanding you have of the problem, the more you can target the problem.
Keep the child's interest. When teaching the child focusing on their learning disability, it can be easy to forget about keeping the child interested in what you're saying. Choose learning material that he will enjoy. For example, if the child likes boats, choose a book on boats.