Dog training never ends. It takes daily practice with your dog and continuous education. Both of which can be simple and fun. You can make daily exercise a game for you and your best friend that strengthen your bond and reinforces basic techniques, boundaries and principals. The education portion can be as simple as reading a dog training book (from the library, store or from a friend), watching a training video on YouTube or enrolling in a puppy training class or dog obedience class. Training and obedience classes are a great way to pick up tips and exercises and most instructors will provide you with an exercise book to refer to at home while practicing with your dog.
You are your dog's very limited world, so you owe it to him (or her) to prepare him (or her) for the world outside the home, take him/her on adventures and spend quality time together each day.
Recommended reading: "How Dogs Learn" by Mary R. Burch, PH.D., and Jon S. Bailey, Ph.D. - this is a complex read so take your time, highlight / mark up and refer to it, reread it whatever it takes to be comfortable with the terminology and fundamentals of the information presented. Grab your book (whatever book you choose), your coffee and put Fido in a settle beside you either on the floor or on the couch and enjoy.