I use the app every day as I can't get to the gym very often. I find it extremely varied and useful.
I stay focused by concentrating on what I want to achieve, and by making sure I do a range of different workouts so I don't get bored. Don't overstretch yourself to begin with - try a few different casual/short workouts and save the ones you like. Add new workouts while repeating the ones you like, and build up the intensity. What are your goals?