Falling asleep is common when you begin meditating. Its ok! Over time and with practice you'll be able to focus more effectively. Meditation is essentially just an intense focus on something of your choosing (breath, mantra, body sensations etc) and you will train your brain to become more focused with time and practice. Don't worry it won't happen the first time, it took me a long time to get better at it (and some days I still can't focus!)