Just before launching iphone6 into the market, Apple has released an official guide on how to transfer files and contacts from Android to iphone.
The guide is divided into sections for E-mail, Contacts, Calendars and includes tips for transferring photos and video: Your music should be imported to iTunes. Books and PDFs will find a new home on iBooks. Moving documents is easy and there is a quick guide on how to find similar or better applications.
For Email, Contacts, and Calendars, you can use Gmail, Exchange, Yahoo, or other similar services. All you have to do is add your Email Account, or use an app like "Copy My Data" for iOS and Android.
Logging in to social networking sites will also import some of your iOS contacts. For photos and videos there are some applications that can help you, but it is not always easy to use a computer for this. Photo Sync application for iOS and Android will be very useful.
To transfer your favorite songs from old Samsung or Nexus,
Apple offers a streaming music app like Pandora or Beats Music.
Detailed information can be viewed here