Introduce and explain. No matter what concept you are teaching, be it addition, subtraction, beginning geometry or something more complex like long division, be sure to introduce the concept first by explaining what it is called and its real life application.
Build on this real life application lesson. After introducing the concept to your student, show how mastery of this mathematical concept will help him in real life. Real life applications always help a student internalize their learning create a sense of ownership over the concept learned.
Use visuals. Many children are heavy visual learners. Meaning, they learn best if they can actually see the lesson in progress. Use an easel, a white board or other visual tool as you teach.
Use manipulatives. Manipulatives are essential when teaching elementary-aged students about math concepts. Kinesthetic and tactile learners also need "parts and pieces" to move about.
Practice. Have your student practice the concept many times with and without your assistance.
Self-check. Teach your student how to self-check his work. If he is unsure of an answer help him right away. Math concepts can take several weeks to master.
Review. Even after your student has mastered the new concept, continue to review as often as you can. This reinforces the learning and helps build upon the next, more complex concept.