what is the best way to train a dog?

Google it...there are tons of methods to train your dog...

You would be wise to invest in a basic obedience course with your dog. Not only will you have professional guidance but you and the dog will likely bond from the close work you do together. Petsmart offers course for around 100 but you can probably find a small local place that offers cheaper course and smaller class sizes.

get him trained by a professional, more like a police dog

there's a book called "no bad dogs" google that.. I lost my copy and I can't write down what I learned here..lol its worth the buy.

If your pet is just a pup,you should start while young by containing it in a large paste board box lined with news paper,and take it out about every 2 hours,let it do its job,then bring it directly back in and don't let it play after job is finished,as it will get confused about why you're putting it out.This way the pet will soon learn that everytime you put it out ,it is suppose to potty.It takes patience,and a strict schedule ,but about two weeks of this and your pet will be potty trained.