First post, hello everyone!
I'm still trying out the trial version of AppGameKit, but have been developing other types of Android apps for 18 months or so. Very excited about the possibilities with this software.
Coming from a rather greyhat background, I know there are a number of pretty effective ways to drive traffic/downloads.
With regard to the Android marketplace, an extensive description is effective, use all 4000 characters. The search algo isn't as advanced as big G itself, so you can get away with stuffing keywords. Use adsense keyword finder to load up every permutation it finds.
Also in the description, be transparent about advertising if it's free, ie if you use push notification ads or content lockers. Explain the permissions and why they're used, so users have a reason to trust you.
Make sure the most recent 3 ratings/comments are good. These are the ones people see on their phones by default. If you have poor ratings, pay for some on fiverr.com or get friends/family to install/rate.
Make sure the package name is relevent to the app, ie it uses keywords.
The above will get the app appearing higher up in search results.
Cross promote your other apps within the app. I don't know how easy this is to do with AppGameKit, but it's a 2 minute job in eclipse to knock up a webview of your marketplace apps.
Somewhere in the app - for example, at the end of a game - pop up the devices native share intents to "soft force" users to share your app. There's also some stuff you can do with the facebook api to get users posting on your facebook app page.
If you've got a website, host the apk's there as well. Use normal seo. Use contentbuzz.com (free) to run automated social sharing campaigns pointing to your website and marketplace listing.
Use fiverr.com to pay for +1's, fb likes/fans/friends/reviews etc. No need to spend a lot to get effective promotion.
Record a walkthrough for youtube. Add the video to your marketplace listing. Create a yt channel for all your app videos. Use vagex.com and u2bviews.com (both free) to get views, subscribers, likes, comments, favourites etc. This will get your videos appearing higher in yt search results and, quite often, an invitation from yt for that adsense profit share thing.
**Blackhat**
Get "mass video blaster" (not free). Spam yt with your videos on multiple accounts. Keyword stuff the descriptions and link to your app. Very, very effective if you can avoid getting too many accounts suspended.
Various other tools found on blackhat forums that can drive mad amounts of traffic. I wouldn't advise using any dubious tools to link to the marketplace directly, instead, use your website as a gateway.
My credentials? None really, but I've been building apps for a while after being in affiliate marketing for around six years, and my very average free apps bring in 3 figures daily from a combination of admob, leadbolt and some others.
Hope this helps someone, or at least sparks some ideas.
Cheers,
Paul.