Aquarium help!?

Ok, I got my self a new aqurarium three weeks ago, and I am really frustrated to see that information regarding aquariums is different depending on the source. In the pet shop I was told that I should wait for 4 weeks without adding any fish, and they would insist, until the nitrite levels drop. In other place I was told to add some hardy fish so ammonia will be produced and the cycle will begin. In other places they recommend a 10% water change every now and then to help the nitrite levels go down and others say that a water change would only slow it down...what the hell? what am I supposed to do here??