First, Know Where to Meet Women
The first key to learning how to approach women is knowing where to meet them. You've probably already learned that it is easier to meet women in some places than it is in others. For example, picking up women in the gym isn't usually a good idea, or at the grocery store or any other place where they're trying to take care of business and don't have time to chat.
Sure, if you see a woman you're crazy about approaching and you know you'll never get another chance, it's better to give it a shot than not do anything. But your chances of getting a positive response will be greatly increased if you go to places where women hang out and relax and where they are open towards meeting somebody: dog parks, coffee shops, book stores, clubs.
Second, the Walk Away Approach
Most men who think they know how to approach women try to go straight from hello to getting a phone number within the first five minutes. The problem with this is that it comes off as needy and it telegraphs interest without giving you a chance to build your social value. Better to make a brief approach or comment, get a response from her, and walk away or get back to your business.
This accomplishes two objectives: first, it shows her that you're not needy and gets her wondering whether or not you're interested in her... and curiosity is easy to turn into interest. The other thing that it does is gives you a chance to test out her response to you and see if you're even interested. Once you've approached and walked away, it's also much easier to come back and engage her again.
Third, Use the Observational Approach
If you're one of those guys who thinks that the secret to how to approach women is having a solid routine memorized before you talk to her, guess again. The best approaches are always the most natural approaches. This means that you have to become a master of using observational conversation starters to engage people.
This isn't as hard as it sounds, the problem is that most guys don't bother to practice this till they see "dreamgirl" and suddenly find themselves reduced to monosyllabic cavemen. You'll never learn how to pick up women if you only test your skills under this kind of pressure.
Instead, practice observational conversation starters with everyone you possibly can: guys, girls, old people, fat dudes you'd normally never speak to etc. This way, your conversational skills will be sharp when you finally see a woman you're attracted to, and you'll be on your game.
Like the saying goes: "The time to repair the roof is when the sun is shining."
Remember, knowing how to approach women is not some magical feat which requires you to summon your spirit guide. Like anything else, it is consistent practice, and these three steps will help you to become master.