I have tried several tools (apps, books, ....). They sounded easy in books, paper and web. In reality not so.
What is distracting you in the first place? Best way is to simply disconnect the internet and turn off the music. Try using Freedom for disabling internet. Have you tried using the Pomodoro technique?
1. decide on the task to be done
2. set the pomodoro (timer) to 25 minutes
3. work on the task until the timer rings
4. take a short break (3-5 minutes)
5. every four "pomodori" take a longer break (15–30 minutes)
30/30 for iPhone and iPad is great for that.