If a woman thinks (you) are "hot" she won't care where you approach her.
On the other hand if you have no idea if she is in a relationship, married, or she has never smiled at you then you might want to take things slowly.
If she is a regular then you can build a rapport overtime by simply greeting her with a "hello" and a smile as you go about your business. After a couple of weeks of doing that you can walk up to her one day and extend your hand to introduce yourself. "Hi I'm ..... I know we've spoken a few times but I don't think we ever really met...etc Based upon how she reacts you can decide whether to engage in more conversation or continue greeting her by name a couple of more weeks and gradually adding more conversation.