How can I make sure I can see my friends in the inner city?

Press F2 while in the inner city, and wait for the dialogue box to appear. Then simply enter their account name into the box - this will let you follow them into their instance, so that whenever your in the same area you'll be able to see each other.

While this feature works most of the time, if the area your in has a lot of players at once your friend instance might be full, and you physically wont be able to join them. If this happens, simply move to a quieter area of the map.