The most important factors when training any dog is to be clear and consistent. Dogs don't do gray very well; it should be black and white. Also if you are not consistent it is going to be much harder to teach new behaviors. Even once a behavior is taught; you need to keep up with consistency. My dogs are very well trained for front door boundaries; but if SOMEONE should allow them to come out on their own or with a word other than their release word then there is fallout behaviors that need a refresher course. Let a bad behavior slide once and you'll get it again.
Educating dogs is all about letting them know what is and is not acceptable. They must learn to respect and listen to you; I see dogs all the time who are wonderful and friendly but do not listen to their guardian. Luke likes to try on the ignore behavior; but he knows it doesn't fly with Mom so he only gives it a go a couple times a year with me. I've seen dogs who literally give no reaction to their guardian; they wander around like no one is talking to them. These are dogs are given too much freedom; to do as they please even if they are pleased to not listen.
It is extremely important to follow through on verbal cues. If you ask your dog to do something you should not just shrug your shoulders and walk away if they don't want to do it. This educates your dog to the fact that they don't have to listen to anything you say. I use please and thank you a lot; but that does not mean there is an option to "not" do what I ask. Training is all about teaching your dog to want to do behaviors, it has to be fun. You can't make a dog do something they don't want to do without physically forcing them and that has nothing to do with educating; only force.
I am always asked about length of time for training and how often? Training should be a never ending process; if you work it into your daily routine then it becomes a way of life. This is much better than having a training session when your dog obeys you and then the rest of the time they do what they please. Of course if you are training for something specific and not just manners then you need sessions for that. If you plan on competing in some canine performance then there will be a lot of extra training just like we would have to do for a competitive sport. But as far as generic manner training; just implement it into your every day. Dogs can do a lot more than we ask of them.