I have a classifieds website...
When users post a new classified, it is automatically added to a dynamic sitemap (xml).
The sitemaps are submitted to google about two months ago, via Webmaster Tools.
Although some classifieds are indexed, it takes way too long for Google to index these.
How does Google decide which sitemaps to index right away?
One example is Stackoverflow questions; They show up in SERP:s almost directly.
Is there anything I can do to make Google index and display my classifieds directly, or is the answer simply: Give it time...?
actually the reason why stackoverflow's answers enter in google almost immediatly, is because this site has a higher PageRank in googles algorithm, meaning it's a "more important" site and will be crawled more for potential new data.
There's really nothing much you can do about it, try making your site relevant, and easy to crawl (read some stuffs about SEO), and hope your site will be picked up in google's algorithm
Google's algorithms will determine how often to crawl your site and when to add you to the index.
The reason Stack Overflow is added so quickly is that Google knows it is a site that is updated frequently with new content.
There are a lot of tricks people will try to sell you to get this, but the only way to really do it is to consistently have good, non-spam content that is updated frequently and wait for Google to pick up on it.
It depends on the importance of your site and the quantity of changes happening on your site.
You can make Google and others aware that you have new content (i.e. a new XML sitemap) using the free service at PingMyMap. It's up to Google obviously to decide when to take the hint...
来源：https://stackoverflow.com/questions/4127935/how-to-end-up-in-google-search-results-within-minutes