Ranking and Measuring
First off, you have to pretty much ignore your game's ranking. It's calculated on the basis of the day's visits alone, which means that a single popular article can propel a midlist game to the top. For example, my game is usually in the 300-400 range of ranking, but recently made it to #4 on the basis of a popular dev blog.
Instead of looking at the ranking, look at your game's number of watchers, which I think is a better proxy for your game's success. Also, don't worry if people don't comment very often - they just don't on IndieDB.
HTML
IndieDB uses a slightly wonky mutant version of HTML with auto-paragraphs and some special tags like [center] and some limits like a whitelist of iframes. Its visual editor is OK, but will mess up any handmade HTML you insert. So in general, when editing a profile or news post, either do everything in the visual editor or everything in the raw HTML. Note that you can absolutely insert custom CSS into your HTML!
Profile
The profile info for your game is the first thing people see, so obviously pick a good banner image. As mentioned above, you can do custom CSS, which means that if you wish, you can make your profile stand out quite a bit, eg like Mount & Blade Warband.
News Stories
Post lots of news stories, one every few days. You can also do features, behind-the-scenes, dev logs, whatever. The number one thing that matters is that they must have lots of pictures. IndieDB staff go through news entries and decide whether a story is shown in the list on the IndieDB frontpage or not. Frontpage articles get many many more visitors than "Archived" ones. And in my hard-earned experience, the one thing that the staff wants is lots of pretty pictures.
Speaking of pictures, IndieDB wants you to choose a massive (1024x768) thumbnail for each story. This thumbnail inevitably gets scaled down to a dinky 120x90 for the listing. In fact, I have found nowhere on the site where it's actually being used at a high resolution. This means your thumbnail needs to look good at 120x90, not 1024x768. I've been known to just give up and scale up small images.
Pictures and Videos
You can also post pictures and videos of your game, and of course you should. These each go into a separate (uncurated) feed on the site. This means it's a good idea to post pictures in groups of about four for extra visibility. On the other hand, don't dump twenty near-identical pictures at the same time, as it will not endear you to the community.