Here's my experience (from Dynamate a 99c app in the games/puzzles category)
The best way to get sales is to have your game at the top of the release list. As soon as it is a couple of pages back then your sales will only be 1 or 2 a day.
To do this, as soon as you receive the email from Apple saying that your game is ready for sale you need to go into iTunesConnect and change the release date to the current date. If you don't do this then your app will be 2 or 3 pages back on day 1!
I've tried getting reviews done (incl. a youtube video) The guys at MobiRiot.com did this for me - Jason did a great job. I think this was worth doing but I didn't notice a massive boost in sales. If I remember, they went to 3 or 4 a day for a couple of days.
I then tried joining all of the various forums and posting to them - this is very time consuming and again didn't generate enough sales worth mentioning.
I've also bought advertising space (banner ad) on one site but again the sales figures haven't jumped up enough for me to suggest doing this. The prices vary massively. Some sites can charge up to $900 per month!
So finally I tried the Lite version of the game, remembering the "change the date" trick to get it on page 1 when it was released and last weekend it had about 9000 downloads. The Lite version has only a few levels and when you beat the last level it has a button that takes you to the Full version in the AppStore. So far this has generated around 90 or so additional sales (about 1% return)
So in conclusion I think the Lite version is the best promotional tool for the least effort. But I think the games category is too competitive now. I have canned the ideas for other games that I was going to do. [shame really Denki Blocks using the accelerometer could have been quite good]
Also how can you compete against the likes of Pangea selling their 68MB 3D console style games for 99c.
Ivan
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Dynamate Lite (free)
WhatBirdNZ (free)