The first thing you should do is create the flashcards for addition. The front should show the equation with the answer on the back. Start with zero plus one all the way up to plus twelve, Then make the "plus one" group starting at one plus zero and going up to one plus twelve. Continue making these all the way up to twelve plus twelve.
Now starting with the "zero plus" group show you child the cards in order saying "zero plus one is one", etc... Then flash them to your child and ask him to read the equation to you and tell you the answer. If he gets them right put them aside. If he gets them wrong put them in a separate pile. When you have completed the first pass go through any that have been missed. Once again putting the correctly answered cards in one pile and the missed cards in another pile. Continue in this fashion until all cards have been answered correctly.
The next day repeat the process listed above with the cards in order, but omit the step where you first go through all the cards first and read them and giving the answer. Continue doing this until the child knows all the facts in order.
Now the next day, shuffle up the cards and have your child repeat step two with the cards in random order. Continue until the child can get all of the facts correct.
After the child has the "plus zero" facts down you will start to teach the "plus one" cards. I still recommend reviewing the plus zero cards daily, but if your child has them down cold that should only take a few seconds. When teaching the "plus one" facts you will follow the same method as the "plus zero facts" First, with you reading the facts, then having the child learn them in order and then mixed. One they have the "plus one" facts down add them to the "plus zero" facts and practice those in mixed order until they can be answered without error.
Next, do the same thing with the "plus two" facts. Of note, once you add the plus two facts you may want to start adding just a few cards each day. First reviewing them separately and then adding them to the pile randomly when learned.
Once your child has mastered addition start with the subtraction cards. Create them exactly as you have for the addition cards. You will teach them in the same way. Start with the "one minus" all the way up to the "twelve minus". As your child learns the subtraction facts add them to the pile of addition facts that he has already memorized.
In this way you will add multiplication and then division facts to the pile. Expect the process to take about a year, but eventually your child will have the math facts memorized. This is the basis of all mathematics and will provide your child with a sold foundation on which to build the rest of their mathematical career.