Still at early stages of my game design but I would suspect the following should be part of a good Marketting plan.
1. A website of your game , a simple one with gameplay videos
2. Gameplay+ trailer videos in YouTube
3. Presence in social networks like Twitter and Facebook
4. Anounce your game 2-4 weeks before it's available in the to generate some buzz
5. Anounce your game throughout iPhone game news site and blogs. Make sure to give promo codes both to the site owners and a few for thier users as part of a giveaway
6. Promo code giveaway to Twitter + Facebook followers as part of rewards to join
7. Discount oro ffer your game for free for a limited time, be sure to announce this as well. I always download games offered free for a few days!
8. Build a great game! A great game advertises itself!
That's all that come to mind ATM