From my experience the following can work if you put in enough effort, yeah some of them are obvious but it's amazing how many people just kick out an app and then do nothing:
- Make sure your category is right, some get more attention that others, if you think you can stretch your say music app over to say the entertainment category you'll get a lot more attention and Apple won't always penalise depending on what the app is (forget secondary categories they do sod all in my experience.)
- Set up a Facebook page and invite everyone you know and share the hell out of posts (try and get enough likes to get a dedicated page name, makes it easier to put the URL on marketing materials)
- Twitter is hit or miss but there's some mileage in it if you can amass enough followers.
- Screenshots on Instagram with the right hashtags and links seems to do well for me at the moment although I cannot really confirm the source of sale.
- Find somewhere in the real world where your target audience may reside and get posters made. Reward the store owners with branded T-shirts, printed media costs very little from places like Snapfish or CafePress and people really like tangible items. I recently took some to my local comic book/game stores for my most recent app. Remember it only takes around 10-15 downloads a day to maintain a position in the category charts (games being the exception) if you can get that from foot traffic it's a good way to build a fan base.
- Find forums or blogs that relate to your app and link drop. Don't just roll in, spam and then disappear, engage with the users. On forums stick a clickable banner in your signature where possible.
- Give out promo codes if the app is paid for. They don't affect app rankings but ask for reviews in return, even if it's friends and family members.
- Gift the app to a handful of people you know (again if paid) you'll recuperate the cost minus 30%
- Write to blogs/sites asking for coverage if you believe there's interest and it's good enough quality to be featured. Many won't reply due to the fact that they're all sponsorship driven these days but if you don't ask you don't get.
- If you have other apps out there, cross promote, just an extra screen with some icons and links can work wonders. If you have updates ready for an existing app, use the update as an opportunity to advertise a new app just be sensible with it so it doesn't feel like spam and always give people the opportunity to dismiss the advert or pop up for good. Never update an app solely for the purposes of advertising another. Trust me this really p*sses people off.
- Run a development blog with screenshots and videos detailing how you built your app, what you found difficult, what neat tricks you discovered, also offer downloadable snippets of useful code. Although sites such as stackoverflow, iPhoneDevSDK and MacRumours offer a wealth of knowledge on coding techniques, you'd be amazed how much help some devs have had from tiny little blogs in the back end of beyond. Remember to link your app in the blog too but don't be spammy with it.
If I can think of anything else I'll drop back with an edit.
