There’s a billion things you can do to market your app and there’s plenty of ways you can spend money to do it. There’s some Apple Marketing Resources you should check out first.
Not only are there helpful tips for marketing your iOS app, but also some guidelines, do’s/don’ts and more that might give you insight into what Apple likes and increase your chances of getting your app featured in the AppStore.
Be sure to check out the iTunes Best Practices Guide also.