How to PROPERLY leash-train a dog? She's new to it?

I've never actually tried to leash-train my dog because she listens so well when we go on walks (we live in the woods in the country too) I just want to leash train her in case we go on vacation to the city or something. How do you PROPERLY leash-train a dog?

http://www.dog-obedience-training-review.com/leash-training-a-dog.html

You may have to follow leash laws in cities where you visit, so your dog definitely needs to be leash trained.

A dog does not need to learn “heel” unless you are planning on entering competition obedience, and heeling is not a fun way for a dog to walk on a leash. Your dog needs to sniff and explore out ahead of you or the walk becomes boring. Do NOT try to keep the poor dog at your side, let him out ahead of you so he enjoys the walk too. You can do that and still have him not pull on the leash

I use a long line for walks, 25 feet long so the dog has a chance to enjoy it. If you have a good recall with your dog, leaving him out 25 or more feet ahead of you will give you control yet letting him enjoy the walk too.