The BEST way to use a Sim is as "Homework" - That is, you spend a day with your instructor, then, instead of having to wait till the next time you are with him, you can go home and practice what he taught you on the simulator so that the next time you are together, you are prepared for the next lesson.

That being said, many people have no chance of getting an instructor. For those people, a sim is the next best thing. It is really not recommended to try learning without an instructor, but if you MUST, and have NO other option, then get very familiar with a simulator before attempting to fly (And keep looking for an instructor)