Recently i got my Adsense approved after much anticipation and planning, this was somewhat of a surprise as opposed to general industry belief that you have to have 1000+ pageviews/day and Domain should be atleast 6 months old so, but in reality nothing is official, Adsense guidelines say that content should have quality and be unique.
Actually i think it's little more than that, its more dependent on the content and how you get your traffic, is the traffic coming from Organic search or not or is it just referral traffic, there are many points which we are going to discuss here, so let's start.

1. Traffic :

Traffic really matters no what what kind of traffic you get ,be it from comments on others blogs or forum signatures, but traffic from some related niche blogs and sites is always considered good, so try to get it.

2. Incoming Backlinks :

Incoming backlinks help you to get traffic+your blog gets indexed easily+chances of better Page-rank, but the link-backs should be properly anchored to get relevant robots to your site and rank only for the related keywords, here is the Complete Backlinking Guide.

3. Organic Search volume and Impressions :

Organic search traffic volume refers to the traffic that your site gets from search engines, i.e. in this case we are talking about Google search, so getting organic traffic is really important, this way Adsense bots come to know of how much impressions our content is getting in SERP's, this is the main reason of  getting approved or not approved many times.

4. New Posts :

If you run a blog and do not update your content regularly, your search engine indexing will be slow and your new content will not get the traffic it should have got if it was related to some latest news, by the time your content gets indexed, the search traffic for that keyword decreases, the indexing rate can be also increased by getting incoming links from good ranking sites which get indexed more frequently.

5. Long posts :

Long posts help to identify your content and sets it apart from many of the copied posts out there, sometimes if your posts are too short the Adsense bots will identify it for some copied content from another big post out there so make sure you always write Medium to Long length posts.

6. Unique Product Reviews :

Generally when people search for review of some Gadget or Service/Product, they generally browse almost all of the results in the first two Pages of the Search results, to make sure the money they are investing in the Product is well spent, so you have to make sure that you write genuine user reviews which are not biased, this will pull the Users to your Blog more often.

7. Good Structure of Blog :

Having a Good structure to the blog lends some authenticity to the content that you are wrieting, likw adding some Page that show who you are, Contact Page, About us Pages etc.

8. Latest Technology and Trends :

Keep you ears peeled out for any new releases and new Gadget Launches, this way you can get enough time to write your content and get good impressions and search traffic, looks out for Trnding Topics on G+ and Twitter for new fads.

9. Don't Apply for approval Repeatedly :

Don't apply for Adsense approval many times, this can cause your account and Website to get blacklisted and you may never again get approved, so only apply for Adsense when you have added considerable content to your blog/site and followed all the above points.

10. Good SEO :

Good Search engine optimization always come in handy to get your content easily up on the search engine result pages, so have a good SEO and if you can afford the help of a good expert then get the help or read some SEO articles to Improve it yourself.