Just a few thoughts for those struggling to get into a routine with meditation:
If you are struggling to meditate at night (when your body is just wanting to go to sleep) try first thing in the morning instead, even if it means getting up 10/15 minutes earlier. You may find you are more receptive and less distracted, and it helps set your intent for the day. Once you are in the habit you look forward to it, rather than see it as a chore. It is the only time I can find in my day when I can be alone, and if I do get disturbed I just try again the next day.
Regarding a focus for meditation, sometimes detailed visualisation can be a bit distracting when you are learning, as you are trying to hold all the details and get it 'right' - simple is best. A single candle flame is good - light a candle and look for as long as you can and then close your eyes and hold the image in as much detail as possible. Mandalas are good to look at as the geometry draws you in through the different layers of meaning, much like stripping away the layers of consciousness.
Personally, I don't like to meditate using outside stimuli as I find them a distraction rather than a help (never tried the app but then i'm a complete luddite). Simply sitting still, comfortably and as straight as possible, and focusing on your breath, without trying to control it, is really all you need to do. I also do chakra meditation but that may not float your particular boat.
If you want a simple visualisation to help you still your thoughts you could try this. Sit comfortably, close your eyes and and breath gently, matching the length of the out-breath with the in-breath. Imagine you are sat on a little wooden platform jutting out into a vast sea. All you can see is sea and sky. If you have a stray thought visualise it as a message in a bottle, bobbing on the sea, and let it drift by. The more often you do this the fewer bottles there will be.
Don't try too hard to achieve anything when you meditate, just aim for stillness and the rest will follow in time.