A key to learning anything new is repetition, so it's important to practice again and again. Insist that he always say "please" and "thank you," or that he takes turns setting the table or be the first to shake hands with adults. If a child forgets to say the magic words, try this tactic: Thank him for his request, and then ask him if he could please repeat it, emphasizing the bolded words when you speak. He will realize that he forgot to say the magic words. If he complains about having to set the table, suggest timing him to see how fast he can get the task done (and make sure neatness counts). If he forgets to put his hand out when meeting someone, gently move his hand toward the other person and help him shake if needed. With persistence, the repetition will pay off, and your child will soon have incorporated these good habits into his daily life.
Manners are an important thing to learn. Having good manners means acting in a manner that is socially acceptable and respectful. Excellent manners can help you to have better relationships with people you know, and those you will steps to take in an effort to develop good manners would be to familiarize yourself with basic etiquette such as dining and phone etiquette. Being polite to others is always a good place to start and you can begin your journey to good manners by holding doors open for others when possible. Good manners convey respect to those you interact with, and also commands respect from those you interact with.