Here are some tips on making your site eligible for ads from google.
Make sure your site has enough and rich content
By this we mean having more than 30 pages of content and being original.
For blogs write up to 25 articles and make sure you have a good SEO score and well organized ideas.
For normal sites, make sure your site has content like pages that explain how your site works and some rules, pricing etc..
Have at least 50 daily viewers
To get a higher percentage into getting in to the AdSense program make sure your page attracts viewers as google can check and know the amount of viewers on your site.
To get that having a good SEO Score is the perfect solution. and also you can try forums and friends
Make sure your site isn't locked
Google needs to access the site without an account, so if your site requires login disable it for a short amount of time and you will get accepted sooner.
You can disable the login and make it so you don't require login for access.