I would try to generate many small, focused apps, try to make them better than average but not obsess about perfection. I would aim for one app every 2 months. You can't predict which ideas are going to take off, so if you generate a lot you have better chances, but be honest and self-critical and don't make shovelware.

You really can "feel it" when the market responds to a good idea, if/when that happens then shift gears and put most of your energy behind that one (for a while).

That's my iOS game/app strategy anyways. I'm a little new to this myself, and it hasn't "taken off" yet, and I've got a lot of work ahead of me, but that seems like what has worked best from watching successful peers.